Your child doesn't merely sit side-by-side with other kids in the sandbox; now he's actually interacting. But what if he only wants to hang out with one kid?

Lots of preschoolers put all their energies into a single friend for a while, says Reandy Just, program coordinator in the child health promotion department of Children's Healthcare of Atlanta, a multibranch hospital. "It shows they're learning to form deeper attachments," she says. The problems start if his friend isn't as interested in exclusivity. Just's own grandson experienced that pain as a preschooler when his main man, Leecy, sometimes wanted a little space. To help your kid cope:

Widen his social circle. Have some other kids over, either for a one-on-one playdate or in a small group.

Hit a different playground. The setting may also encourage him to approach some potential new pals.

Ask his teacher for help. If she sees him glomming on to one child, she can guide him to a different play area, where he'll mingle with other kids. It'll give both kids a break, which just may be the best thing for their friendship after all.