If you've ever marveled at the look of concentration on the face of a child who tries to fit a square block into a square hole or catch a ball in mid-air, you know that playtime isn't just about fun and games. It's serious business — and toys are the tools of the trade.

Here is an age-wise guide to how kids play, and to the toys that entertain and help kids understand the world, learn social and emotional skills, and stimulate a developing brain.

Babies: How They Play

Play in the first year of life is all about exploration. Babies use their five senses to learn about the interesting new world around them: Does an object feel hard or soft? Sticky or rough? What does it do if I drop it? Or put it in my mouth? Most play consists of "tasting" or mouthing an object and shaking, banging, or dropping it.

When your baby develops new motor skills, play becomes more coordinated and complex. For example:

• At about 4 months old, babies begin to reach for and grasp objects, like a rattle.
• By 6 or 7 months, they can transfer that rattle between hands.
• At around 9 months, a newly developed pincer grasp makes it easier for babies to pick up smaller objects, like blocks and other small age-appropriate toys.

During this time, play is usually a solitary activity, but playing side-by-side with other babies and imitating activities is common by year's end.

For now, you are your baby's favorite playmate. Have you ever danced a puppet in front of your baby's face, only to have him grab it and pull it toward his mouth? Or has he ever squealed in anticipation and delight when you creep toward him, saying, "I'm gonna get you!"

These interactions help your baby learn about language, social relations, and cause-and-effect. Once babies begin to understand how things in the environment relate to each other and how they taste, smell, feel, and sound, babies are ready for the next stage of development: figuring out how they work.

Smart Toys for Babies

• Nursery mobile. Objects dancing above a baby's head while lying in a crib stimulate vision and develop attention span.
• Mirror. Initially, your baby will be fascinated with the changing face and expressions looking back from the mirror. Over time, your baby will realize that the drooling, smiling baby staring back is actually a reflection. Once this happens, babies become aware of themselves, which leads to more self-discovery as they learn about body parts and where they are.
• Ring stack. This classic toy features a cone that fits different sized colored rings. At first, babies enjoy holding and mouthing the rings. Later, they practice fine motor skills by fitting the rings onto the cone. Toddlers also learn about colors and numbers when you count the multicolored rings as you stack them.
• Push-pull toys. These help with balance and large-muscle development as your little one goes from a couch surfer to a walker. The more babies push and pull, the more they work the muscles necessary to turn them into runners and climbers. Later, in the toddler years, kids can use them to help control their increasing speed.

Toddlers: How They Play

Toddlers are becoming aware of the function of objects. They like to stack blocks, babble into a toy phone, or drink from a "big kid" cup. The concept of pretend play starts now. Your little one might tuck a baby doll into bed at night or make "choo choo" noises while pushing a toy train.

This lays the groundwork for preschool play, when using the oven timer in a play kitchen or ringing the bell in a pretend fire truck signifies your child's growing understanding that each item serves a purpose.

Your toddler also will begin to differentiate colors and shapes. So choose toys that are bright, colorful, and fun for little hands to hold. By age 2, most toddlers can kick a ball, scribble with a crayon, and build towers four or more blocks tall. By age 3, they can do simple puzzles and pedal a tricycle.

Expect to see a lot of repetition, as that's how little ones master new skills and learn they have some control over the world around them.

Smart Toys for Toddlers

• Balls. Whether they're bounced, rolled, caught, or thrown, balls encourage gross motor skills, hand–eye coordination, and dexterity.
• Shape-sorting toys. Pegboard puzzles, nesting cups or blocks, and buckets with holes for different shaped blocks challenge hand-eye coordination and problem-solving skills.
• Mechanical toys. Pop-up toys and "busy" boxes with knobs, buttons, and levers encourage fine motor skills and problem solving, and teach cause-and-effect.
• Role-play toys. Play kitchens, doctor's kits, and golf sets help children learn how the world works by imitating the actions of you and other influential adults. Dolls and stuffed animals encourage pretend play (a tea party for teddy bears, perhaps?) and aid social and emotional development by teaching tots how to express emotions and take care of something they love.

Preschoolers: How They Play

Babies explore objects with the five senses. Toddlers start figuring out how they work. Now, as preschoolers, they'll use toys and other objects for their intended purpose, yet also will imagine a world of other possibilities for them. A blanket thrown over a coffee table becomes a secret clubhouse. Modeling clay can be used to make pizza pies that you're asked to "taste."

For a preschooler, the world becomes a magical place without limits — and preschoolers are the masters and creators of it all. Many kids this age think they have magical powers and can battle "monsters" and win, or turn into a princess, fairy, or other whimsical creature.

Often, your preschooler will pull you into a fantasy and expect you to play along. It's also during this time that imaginary friends may "appear." This type of fantasy play is crucial to kids' development because it helps them work on their fears, anxieties, hopes, and dreams.

The world is also a stage, so expect to hear lots of "mommy, daddy, watch!" as your preschooler learns one new trick after another and seeks your approval and support for new accomplishments. The desire to connect with others extends to friends as preschoolers begin to learn the give-and-take of cooperative play and sharing.

Pretend play becomes more elaborate. Kids' knowledge of the world is more advanced, so don't be surprised if your preschooler knows exactly how to work electronic gadgets or make electrical toys (like a radio-controlled car or a video game) work.

Play itself becomes more physical. Why just walk when you can hop, jump, or skip?

Smart Toys for Preschoolers

• Arts and crafts. As fine motor skills improve, activities like holding a crayon, drawing pictures of family members, and using a pair of safety scissors to cut and paste strengthen coordination, encourage creativity, and foster self-esteem.
• Blocks and construction sets. Building a tower (and figuring out how to stop it from toppling over) encourages problem-solving skills and hand–eye coordination. Preschoolers use their imaginations to create buildings, vehicles, animals, and more from simple construction sets.
• Puzzles. Jigsaw puzzles help with coordination and dexterity, and teach about spatial relationships (where things are in relation to other things) and logical thinking.

Big Kids: How They Play

Elementary school-age kids are accomplished in ways they never were before. They've grasped an understanding of the world around them and are now moving toward mastering skills that once challenged them, like catching a football or braiding a friend's hair.

This also is the time where talents and interests take hold — a 4-year-old who enjoyed story time may grow to love reading; a 5-year-old who listened to music might want to play piano.

Physical abilities, like large and fine motor skills, are being refined. Children learn to ride two-wheel bicycles and glide on skateboards. Arts and crafts become more intricate, and a child might spend hours weaving friendship bracelets or drawing comic strips.

Peer relationships take on more importance, and your child might be more interested in playing with classmates than with you. But remember that even as your child matures, you are still the most important playmate — so try to carve out some one-on-one time. Family game nights are one way to get everyone together.

And now's the time to try new adventures, such off-road biking, that kids couldn't do when they were younger and need your supervision to do safely now.

Smart Toys for Big Kids

• Jump rope. By skipping rope with friends, kids learn to take turns and get along with peers. All that jumping, and the coordination it requires, encourages large motor development and problem-solving skills.
• Card and board games. Card games like "war" or "crazy eights" and board games like checkers or chess teach about strategy, turn-taking, negotiating rules, and fair play. Encourage cooperation and help your child learn to manage the emotions that come with winning as well as losing.
• Musical instruments. Learning to play the piano, violin, guitar, or another instrument encourages listening and fine motor skills and helps build attention skills.
• Science toys. Chemistry sets, binoculars, telescopes, or other toys that promote discovery and problem-solving help improve math and science skills, and help develop imagination.

The Perfect Toy: You

A baby staring at a mobile; a toddler stacking blocks; a pre-schooler painting with watercolors — all are activities that can be done independently.

But don't underestimate your role. After all, it's you who put up the mobile, turned it on, and encouraged your baby to follow. It's you who first showed your baby how to stack those blocks. And when you sit side-by-side with your kids and paint, color, or read a story, you give them the attention they need to build their self-esteem and feel loved and secure.

Toys are a tool to help kids develop, but it's parents who nurture that growth.