My 21-month-old son is all boy. He's obsessed with cars -- his toy ones at home and the real ones out on the street. He loves playing ball. He walks with a swagger, his cute little belly sticking out. He eats like a horse. He bats his eyes and flashes his adorable dimples at the girls, little ones and the grown-up kind.

But he also plays with girls' toys -- tea sets and bracelets and Minnie Mouse dolls and makeup. And he sometimes even wears girls' clothes.

It's not his fault. He has a sister. And because he's our second child, that means sharing playthings and wearing hand-me-downs, gender-appropriate or not. It would all be fine and good, except that his grandparents -- my in-laws -- are pretty horrified about the whole situation.

Let me give you a little background. My mother- and father-in-law are loving, wonderful people who adore their grandchildren. But they believe in girls' toys and clothes for girls and boy stuff for boys, to the extreme. Think Disney princesses and Dora and Hello Kitty and frothy, frilly pink outfits for baby girls, and Disney pirates and cars and balls and blue, blue, blue everything for baby boys.

One cold, wintry night, we Skyped with them after the kids were in their pajamas and about to go to bed. My little boy had run out of the few warm footie PJs he had -- they were all in the wash. So we resorted to dressing him in one of his sister's sets instead. It had pastel-colored polka-dots all over it. It was girly. He didn't know the difference. My mother-in-law, on the other hand, did.

"What in God's name is he wearing?" she asked, incredulous, squinting at the screen. I laughed uncomfortably, knowing what she was thinking. "Oh, that's just an old set of pajamas of hers -- his are all in the laundry," I explained, hoping it would be left at that. It wasn't.

"Catherine, he's a boy," she reminded me in a scolding tone. "You have to dress him like a boy. He shouldn't be wearing girl anything!"

I thought about defending myself, telling her it was no big deal, because my son -- her grandson -- was still very much a boy, despite the trauma he was no doubt experiencing by wearing his older sister's pajamas to bed once in a while. But I decided to bite my tongue and just nod as though I understood the big reaction and the alarm. I was just glad she hadn't called when he was playing with his sister's pink tea set.

Look, I am not one of those parents who deliberately tries to turn gender roles upside down with my children. I want my son to look and act like a boy and my daughter to look and act like a girl. But, for one thing, there are so many different ways boys and girls act. And for another, the fact that my little boy sometimes wears girls' clothes and plays with girls' toys -- and my little girl sometimes wears her brother's outfits and plays with his toys -- is probably not going to scar him (or her) for life, or confuse them about their gender identity either. Truth be told, they probably won't even remember it.

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I understand that their paternal grandparents -- and plenty of others out there -- are uptight about this sort of thing, and old-school about what young, impressionable girls and boys should be wearing and doing. But I wish they wouldn't make such a big deal out of it. There's something to be said for a little boy with a sister, and a little girl with a brother. They grow up understanding each other and the opposite sex in a way that children with same-sex siblings don't. And that's a good thing.

Are your child's grandparents uptight about anything? How do you deal with it?