Boys play with boys, and girls play with girls.

At least that’s what I’ve come to expect.

But when my son entered preschool at the tender age of 20 months, he was surrounded by a sea of little women. The trend continued throughout his preschool years. Whether the XY chromosome was in short supply in 2002 or some other factor was at play, I don’t know. What I do know is that my son likes playing with girls. Always has. Still does.

That said, he’s not big on dolls. He puts little stock in playing house. He loves the sports page, scary sharks and could play soccer or street hockey all day long. In short, he’s a guy’s guy.

But he’s also a girl’s guy. Some of his best friends are girls, long past the age when opposite-sex friendships have usually fizzled. By some unwritten contract, they manage to eschew princesses and dinosaurs and find common ground. They pretend to be doctors or sailors or explorers. They color or challenge each other to a Zingo match.

So it makes sense that I expected the trend to continue with my second child, a girl. Since her most frequent playmate is her brother, I figured she wouldn’t discriminate.

I was wrong.

Two weeks ago, she turned 4. We celebrated at a meticulously orchestrated Fancy Nancy extravaganza. Fancy Nancy, for moms of boys, is a girly-girl popularized in a series of books who likes to speak French and wear tutus and is horribly embarrassed by her oh-so-plain parents and brother. She uses fancy words, like fuchsia, and munches on fancy food, like tea sandwiches.

At my daughter’s party, invitees traipsed from station to station: glittery make-up was brushed onto their cheeks, glittery nail polish sparkled on their fingers, glittery sticker earrings were pressed onto their earlobes.

The diminutive guests arrived in their fanciest attire – fake pearls and high heels, princess ball gowns and magic wands. As favors, we handed out jewel-encrusted tiaras.

Pink strawberry cake was served, and Shira leaned toward me and said, “Mama, I love this party.” By the end of the evening, she was already planning next year’s fiesta, same theme, different stations.

It goes without saying this was not a boy-friendly bash. I felt guilty about not inviting the boys in her preschool class, especially since she’s invited to all their parties. But this was what Shira wanted. She was the birthday girl; she got to choose.

It makes me a little sad that this is what happens to most kids. They get older and they choose to stick with their own kind. I know it’s developmentally appropriate, but it’s also bittersweet to watch formerly fast friendships fade away.

Boys will be yucky, and girls will be gross for about 10 years, until one fine day, when voices have deepened and curves have developed, they’re not.

Bonnie appears Saturdays on TriangleMom2Mom.