Play is the business of childhood; allowing your child free rein to experiment with the world around him and the emotional world inside him, says Linda Acredolo, professor of psychology at the University of California at Davis and coauthor of Baby Signs: How to Talk With Your Baby Before Your Baby Can Talk and Baby Minds: Brain-Building Games Your Baby Will Love. While it may look like mere child's play to you, there's a lot of work - problem solving, skill building, overcoming physical and mental challenges - going on behind the scenes. Here are some of the things your child is experiencing and learning, along with ideas on how you can help boost the benefits of his play.

Play builds the imagination
Pretending or imaginative play, is one of the cornerstones of a young child's world. Children begin demonstrating this behavior around the age of 2. Almost anything can spur your child's imagination, including everyday objects. This is because they use them as symbols; they are learning that one thing can stand for other things. Using this new ability to pretend, they can transform a block of wood into a boat, a few pots and pans into a drum set.

Everyday objects aren't the only things that are transformed in your child's make-believe world. So are the roles they assume in their play. They'll move from superhero to baba to police officer to ammi and doctor with ease. By experimenting with diverse jobs and identities, they are able to explore a variety of scenarios and outcomes. Sometimes the stories they acts out reflect issues they are struggling to understand. If they are coming to terms with a new sibling, for example, they may incorporate a lot of nurturing behavior into play, mimicking your interaction with the new baby. Imaginative play gives your child a sense of control as he/she interprets the dramas of everyday life and practices the rules of social behavior.

Play promotes social skills
As toddlers, children play side by side without obvious communication (this is called parallel play). During the preschool years, they start to interact with each other by creating complex story lines together. As they do this, they learn to negotiate, cooperate, and share (though some children don't master the art of sharing until they're 4 to 6 years old). When children disagree about who gets to be the daddy or who will wear the purple dress, they're actually developing important social skills.

How you can boost social play: Once your child settles into preschool, he'll find playmates there. But he'll need your help to extend those relationships outside of school. The easiest way to build newfound friendships is to schedule play dates or set up a play group for your child and his friends. Get the ball rolling by introducing games or activities and then unobtrusively monitor the children's behavior and progress. After the play date, you'll know which social skills your child is mastering (sharing, cooperating, or being assertive, for example) and which he may need some help with.

Play advances physical development
Different types of physical play help develop different skills: Skipping takes balance, for example; climbing monkey bars builds strength; and sports activities involve coordination. Large motor skills, such as running, throwing, and pedaling, improve first, but fine motor skills aren't far behind. A 3-year-old carefully stacking blocks into towers is not only learning about gravity and balance but also developing hand-eye coordination. And the dexterity your child develops during play carries over into everyday life: After some practice, a 3-year-old will be able to help dress and feed himself, which gives him a sense of independence.

How you can promote physical play:
The best way to get your child moving is to set a good example. This starts at home by engaging in physical activities rather than sedentary ones such as watching TV. Indoors, you can play hide-and-seek, toss beanbags, or play some danceable music. Outdoors, build a castle in the sandbox, kick a soccer ball back and forth, ride your bike/tricycle together.

Play helps children work through emotions
Long before children can express their feelings into words they express them through physical play, storytelling, art, and other activities. When children have experiences that are hurtful or hard to understand, they review those experiences again and again through play. For example, if your child is pushed or has something snatched away from him at school, he may not understand what just happened. If, the next day, you're playing with him and he aggressively pushes you, he may be trying to work out what he experienced the day before.

How you can help:
During play, your child will expose little bits of behavior he needs guidance with or doesn't understand. You can respond in kind, mimicking the right type of response. And try to get your child to laugh, which will help ease tension.

Your role when playing with your child
It is helpful to allow your child to lead during play. "Let your child determine what to do and how to do it within the limits of safety and time constraints," she says. "This lets him try out his judgment and allows him to show you what he's delighted in." Join in your child's play, but only when invited to do so. As he lets you into his world of make-believe, give him complete control. In real life, you may be in charge, but this is his world.

The attention you show your child when you play together is the key to building his self-esteem. For example, when you pretend along with him, you are showing him that you accept his make-believe world, that something he's interested in is fun and important to you, too.