Friends offer opportunities for a child to try out different aspects of her developing personality: her likes, dislikes and ways of relating.

She must learn how to socialize, to give without expecting an equal return, to share, to elicit positive responses and to care about someone her own age.

She can use friendship as a safe haven, and as a mirror. She can try out different styles and new adventures through the encouraging eyes of a friend. In the process, she’s learning about herself, and about how to attract and hold onto a friend.

A friendship’s necessary give-and-take is different from relationships with parents and siblings.

A child without friends is a poor child indeed. While a child must learn to deal with her own temperament — for example, her shyness or high activity level — it’s even more important for her to learn how to adapt to the demands of a group. A friend who is like her will help her do this. It has always intrigued me to watch two small children play and learn from each other.

When should parents start introducing a child to other children outside the family?

In the second year, it becomes important for a child to learn how to cope with other toddlers. In a large family or in a busy neighborhood, she may already have begun to learn about sharing, rivalry, teasing and coping with older children or a new baby.

But the kind of relationships a child can make with children who aren’t her age are different from those she will make with her peers. Older children tend to protect, tease or overpower younger ones.

In healthy peer relationships among toddlers, children first learn the give-and-take of equality. They learn the rhythms of reciprocity — when to dominate and when to submit. This is basic to important relationships in the future.

In the second year, children are both demanding of others and learning to be sensitive to their needs.

Just watch 2-year-olds at play. If parents set up regular play groups of two or three toddlers, they can all learn about each other.

At this age, learning occurs by imitation. In so-called parallel play, two toddlers can putter alongside each other without ever appearing to look at each other. And yet, they’re already far more interested in and capable of learning from each other than the concept of parallel play would suggest.

Each child imitates the other with entire hunks of behavior. This ability to pick up and imitate whole sequences of a peer’s activity is astonishing at this early age. As one toddler stacks a row of blocks to make a skyscraper, the other will stack the same number of blocks for her building — using similar gestures as she does so.

I’ve seen 2-year-old children absorb whole new sets of behaviors from other 2-year-olds and perform tasks to which they had never before been exposed.

What if toddlers aren’t able to get along? What if one is too aggressive and overpowers the other, who is temperamentally a quieter, more reserved child? Is it healthy for either of them? Not really.

The parents of these unequally matched children will likely be drawn into taking sides and risk reinforcing each child’s imbalanced behavior.

When parents of toddlers get into their children’s play, they risk changing it entirely to an adult-oriented occasion. The opportunity for the children to learn about each other is diminished.

Here are some tips to help create balanced friendships:

• If the children can’t right the imbalance on their own, find another child more your child’s speed. If possible, find a playmate who’s suited to your child in temperament.

• If your toddler is a quiet, thoughtful, rather sensitive child, try to find one like her. She’ll learn a lot more from a peer who is learning to handle a temperament like hers than she will from your urging her to be more aggressive or gregarious.

Though you mean to encourage her when you rally a hesitant child to fight back or to act differently, she will sense that you don’t approve of her as she is. Her self-image is at stake.

• If your child is aggressive and impulsive, look for another like her. They’ll build up to peaks of frantic activity but will probably find ways of subsiding. In this way they will learn — gradually — about not overreacting to their impulses.

After playing together regularly two or three times a week, such children will eventually become bosom buddies and will be learning as much about themselves as about each other.

Questions or comments should be addressed to Dr. T. Berry Brazelton and Dr. Joshua Sparrow, care of The New York Times Syndicate, 620 Eighth Ave., 5th Floor, New York, N.Y. 10018. Questions may also be sent by email to: nytsyn-families@nytimes.com