I actually disagree with the "kids really get us" comment.
Children between the ages of 3 to 6 are first learning about sex differences. As young children who only see black & white, they can be extremely harsh and rigid in how they adopt the social constructs of gender. And they are incapable of explaining or understanding what makes someone a man or woman except through biology (you have a penis, you don't) or via blatant sex stereotypes (you have long hair and wear a dress or don't).
Researchers looking at sex and gender differences in children in North America have found that even when adults try to adopt and teach broader norms of gender expression, children within that age group often reinforce sex stereotyping amongst themselves. Meaning: adults can teach the kids that boys can play with dolls,have long hair &wear pink and girls can play with trucks, have short hair, & wear blue, and many of the kids themselves react very strongly against this when they play and interact with each other. In Western culture, children are basically bombared with sex stereotypes as an explanation of gender, and the vast majority aim to "police" those around them to follow these constructs.
The reason that young children often view us as our gender correctly is not tha they are innocent and pure and see our true nature. It is that many of us are deliberately projecting/sending sex stereotyping messages in some of the most superficial ways: how we dress, wear our hair, etc. It is working with these kids. You wear boy clothes and a boy's hair cut....bingo...you're a boy!
Absolutely nothing wrong with this, and I get that it feels good when it happens, because passing is passing. But I caution people into reading too much from how a 5 year old view your gender, because as much fun as 5 year olds can be, if we reinforce their assessments of our gender, all we have done is tell them that sex stereotypes are right & that they should feel they have to conform as well with a framework where boys wear short hair, pants and blue, girls wear long hair, dresses and pink.
