My wife and I count two different gay couples — one lesbian, one male — among our closest friends. We see these friends often, and they are important people to our two young daughters.

On Sunday we saw both couples. In the morning the women came over to celebrate our daughter’s second birthday. We ate cake and drank coffee on the roof deck while the children played. Later that day we went to the guys’ house for dinner. There we ate more cake and drank beer while the children ran around the backyard with the two dogs.

On the drive home our three year-old must have suddenly for the first time grasped the essential difference between gay and straight. From the back seat she asked me and my wife, “Why are some sweetie-pies men and men? Why are some men and women? And why are some sweetie-pies women and women?”

The ease of that brief conversation left me with a rare kind of satisfaction. My kids inhabit an America that is by one measure far more humane and decent than the one where I grew up.

I must have been about twelve when I learned that my mother knew a lesbian. She refused to name this person when I asked who she was. Did I know her? Had I met her?