And the more they do, the deeper the habits grow, according to a study in the May issue of Developmental Psychology. And this split might even influence how they behave later in life because they grow up with different sets of expectations, social skills and other habits, says the study.
For instance, girls together increasingly play more quietly, closer to teachers, usually with dolls, dress-up and the like, while boys fan out in aggressive, rough-and-tumble games, far from rules and authority figures.
"The pattern is very strong, very, very strong. It's a very, very sexually differentiated pattern of play. It's very stable over time, and the consequences seem to be exaggerations of gender-related roles over time," says the study's lead author, Carol Lynn Martin, a professor in the Department of Family and Human Development at Arizona State University in Tempe.
Martin and others studied 61, 3-to-6 year olds for six months at a university preschool. Watching at 10-second clips, researchers recorded more than 20,000 observations of the children, examining their play partners and activities. What they noticed overall: At the beginning of the study, boys and girls behaved about the same at play; at the end of the study sex differences were more pronounced.
About 82 percent of the boys played mostly with other boys, and of these, 35 percent played with boys 90 percent of the time, the study says. Just three of the study's 28 boys played with girls more than boys. Generally, the boys' play displayed predictable characteristics, Martin says.
"You would see them running around, and they do what's called 'call to the chase'," Martin says. "The boys will kind of go up with a little bit of teasing and taunting, 'come chase me,' and run off, and then another little boy will follow."
"Boys tend to take up more space on the playground," she added.
Girls are even more gender-specific. About 90 percent of girls play with girls more than boys, and 45 percent of these play with girls 90 percent of the time. Only one of the 33 girls played more with boys.
"The girls tend to be more quiet and more cooperative," Martin says. They play close to teachers, she says. "They could be doing art, dressing up."
As the observers watched over the course of the six months, children increasingly played with their own gender, Martin says. And the more they had played with their own gender early on, the more deeply gender-divided their play was. Boys roughhoused more while girls played more calmly and cooperatively. This "dual polarization," as Martin put it, meant the two groups were less and less likely to want to play together. Girls, she says, tended to avoid the boys' rough play.
Younger children are certainly less likely to play only with their own sex than older kids, says Margaret Boyd, director of the Jesse Lee Nursery School in Easton, Conn. Boys run around a lot, Boyd says. If the play grows too wild, the teachers need to rein them in. "And the girls do a lot of imaginary play, like school, or mommy and baby, or doggy and kitty."
Sometimes, Boyd says, the sex-segregated groups interact in an interesting way. "They play boy-girl games, chase games, where the boys chase the girls, in a big circle."
Where will this take the children long-term? "Time spent with same-sex peers sets powerful forces in motion that affect children's subsequent development," Martin wrote in the study, but she said later she doesn't want to blame the differences between men and women on early childhood play practices. Boys with more aggressive play practices seem to have more difficulty adjusting to elementary school, she says, and this may be the start.
The social split between the genders seems to begin at about 2½ for girls and 3 for boys, Martin says, and no one is sure why it begins. Researchers believe genetic differences between the sexes is only responsible for a tiny percentage, she says. Perhaps something as small as a slight activity level difference between boys and girls becomes exaggerated over time, she says. Children dubbed "gender police" by researchers help create stronger divisions by establishing "girl" activities and "boy" activities, she notes.
"I'm certainly curious whether these things will hold later," she says.
Parents interested in eroding some of the divisions should take heart, Martin says. Providing play dates where girls and boys can play together, preferably at structured activities with adults nearby, seems to encourage more cooperative play between the sexes. Learning they share interests and are similar seems to help break down barriers, she says.
At Jesse Lee in Connecticut, Boyd says, it's easy to bring the two genders together in class. "If we bring out games, they all want to play," she says. And then, she says, the boys and girls cooperate very well.
"It's better for both sexes to have some opportunities to play with the opposite sex," Martin says.
What To Do
For recent research on preschoolers, take a look at previous stories on HealthDay.