Magnus is officially taking this conversation very seriously. When he thinks of it as an important big-brotherly moment, it stops being something to blush about and becomes something to just... walk Sunny through as clearly as possible. "Yeah. The way I learned it, boys have penises and girls have vaginas. That's not... universally true. Some girls have penises and some boys have vaginas. Some people have both. But penises usually come with testicles, and are the ones you can stand up to go potty with. Vaginas usually come with uteruses and ovaries, and are the ones you sit down to go potty with."

It's probably too much to explain that pee doesn't come from a vagina, right? He can do that after the first round of explaining?

"People who have ovaries inside will, um, lay their eggs through their vaginas, but not until they're teenagers. I'm guessing one of the girls here will help explain that whole process to you when you become a teenager, since I'm pretty sure you're the only person in our family with a vagina."

A sudden mental image flashes through Magnus's mind, though, of him and their dads poring over the What's Happening To My Body? Book For Girls or The Care and Keeping of You and taking very detailed notes, and for a weird little moment, his heart clenches. It's nice, to think of their little family having a long and caring future.