It's Tuesday morning—time for my two-year-old daughter's weekly play date with her friend Madeline. The girls greet each other at the door with an enthusiastic "Hi!" but within minutes, they beeline to opposite sides of the room. After that, except for the occasional tug-of-war over a toy, they hardly notice each other until it's time to say goodbye.

Madeline's mom and I exchange a frustrated sigh. We keep hoping that our charming, chatty, book-loving daughters will bond, but so far, they seem more interested in each other's toys than each other.

Is age two too soon for children to start building friendships? Are play dates a waste of time for toddlers? Not at all, says Cathi Cohen, LCSW, a Fairfax, Virginia-based therapist specializing in children's relationships and author of Raise Your Child's Social IQ. "In the toddler years, and even in infancy, you're setting the stage for socialization," she says. "You're helping your child learn the social cues she'll need for making friends."

For some children, making friends comes as naturally as breathing; but for many, it's a learned skill gradually acquired over time. You can help by offering gentle, age-appropriate guidance, and lots of opportunities to practice the positive behaviors that will make your child a welcome member of his or her peer group, right from the start.

By the time your baby is just a few weeks old, he's already starting to pick up social cues. You'll notice that he tries to capture and hold your attention by smiling, giggling, and cooing—and he does this more with his parents and siblings than with strangers. Already, some people are more important to him than others.

Actual friendships, though, are fleeting during the baby and toddler years. "Friendships are very situational at this age," Cohen says. "It's 'I'm here and you're here, so you're my friend.'"

Don't worry if your toddler doesn't actually play with his playgroup buddies. At age two, you'll still see what's called "parallel play" —children playing near each other rather than with each other. It's still beneficial for your child to be around other children, to see how they move and relate and share the same space, Cohen says. That's how children begin learning how to get along with their peer group. Around age three, they'll start actively engaging each other.

Friendship-Building Tips for Toddlers:

• Toddlers who have siblings and those in daycare tend to acquire social skills earlier because they practice them daily. If you're a stay-at-home mom or have an only child, it's a good idea to head to the library, playground, or a mom-and-tot class to give your toddler a chance to interact with his peers.
  
   
• Toddlers are naturally inclusive, so group play dates are fine at this age. Your child probably won't show any special preferences for one friend over another yet. She'll view all other toddlers as potential playmates.
  
   
• Before every play date, hide any toys your toddler won't be comfortable sharing. If a battle over Chicken Dance Elmo is going to result in a tantrum and tears, it's best to keep Elmo out of sight for the duration.
  
   
• Encourage positive social skills through your words and actions. Tell your toddler what you expect, and demonstrate when possible: "We say please," "Let's share," "We take turns," "We don't hit." Don't be discouraged if your toddler doesn't follow these rules yet; most won't. But with time and experience, your child will get the idea and start to follow your example. Learning good social behaviors now will make it easier for your child to form friendships in the years ahead.

Around age four, children become more selective in choosing playmates. This is when behavior begins to play a role. Four-year-olds will seek out friends who exhibit positive behaviors such as gentleness and sharing, and avoid those who display negative behaviors such as hitting or grabbing toys.

Children this age also begin to choose their friends based on common interests. A child who likes playing with dolls will make friends with others who like dolls, while a child who prefers trucks will make friends with others who share that interest. Gender differences, however, don't often matter to preschoolers. Boys and girls happily mix and form friendships at school, in playgroups, and at birthday parties.

Friendship-Building Tips for Preschoolers:

• By age four, it's best to focus on one-on-one play dates, Cohen says. If you invite more than one child over, you risk creating an "odd man out," leaving someone with hurt feelings. This is a good age to learn the concept of loyalty to one friend. If another child asks to come along, your child can politely say, "I already have a play date today, but how about another time?"
  
   
• This is also a good age to seek out playmates with common interests. If your daughter is athletic, invite other athletic girls over; if she's quiet and bookish, other quiet, bookish kids are a good bet. Similar temperaments and shared interests will make a promising foundation for long-lasting friendships.

In kindergarten, your child will narrow his pool of potential friends even more. By age five, children not only seek out friends based on positive behaviors and shared interests, but gender. In fact, gender suddenly becomes the Grand Canyon that separates girls from boys. "It just naturally occurs," Cohen says. "You might see a bit of it in preschool, but it's very marked in kindergarten."

So don't be surprised to hear your son and his friends say, "We don't like girls!" or your daughter claim, "Boys have cooties!" And if you're planning a birthday party for a five-year-old, consider making it all-girl or all-boy.

Kindergartners also tend to change friends frequently. It's not until third or fourth grade that friendships become long-lasting, and you can expect your child to have the same friends from year to year. For now, don't worry if your child seems excited about a different friend every week.

Friendship-Building Tips for Kindergartners:

• Your child is now old enough to practice being a good host. When a friend visits for a play date, the host should let the visitor decide what to play.
  
   
• Limit any play date time spent on videogames or TV. (Try using a kitchen timer.) Children who are interacting with a video screen are not interacting with each other. Try setting out a planned activity ahead of time—a board game, a craft project—that the children can enjoy together. Give them the chance to stretch their imaginations and practice their social skills.

Friendship is about more than just child's play. Your child's ability to get along with her peers can contribute greatly to her happiness, in school and in life. By offering a few gentle nudges in the right direction, you can help her learn the positive social skills she needs to succeed.