Have the children get into pairs. (Children younger than 4 or 5 will have a hard time with that instruction—I tell them “find a friend to hold both hands with,” and that makes it a little more concrete.) If necessary a child can pair with an adult, but it works best if you’re about the same size as your partner.
The rule is, when the grown-up calls out a body part, children have to touch that body part to their partner’s. I always start with “back to back!” and they touch their backs together. “Belly to belly!” “Head to head!” etc.
Almost no matter what, everyone’s laughing in a minute. You can get as complicated as you want, depending on the group of kids. “Fingertips to fingertips!” “Chin to chin!” “Heel to heel!” And try doing “Nose to nose” without giggling—can’t be done. Same is true of “Bottom to bottom,” of course.
When it’s getting time to finish, I always end with “Whole body to whole body!” which gets everyone hugging (awww!), and then transition with “Bottom to floor,” and they all sit down.
This game is obviously great for social development. You build bonds with other people by laughing with them and being physically close to them, and you build cooperation skills by coordinating your movements with each other. There’s also some physical development and learning in there: you build balance and coordination and body awareness (especially if you throw in some more esoteric body parts—shoulder blade! knuckles!). It’s a good transition game: at the beginning of circle time it takes all their disparate energies and gets them focused in the same place and paying attention; at the end of circle time it uses some of their pent-up energy from sitting and gets them ready for the next thing. It’s also a good “party” game—fun to break out when there’s a birthday, for instance. And parents think it’s the cutest thing ever.