"Mom, why do boys' voices change and girls get boobs?"
"Ah. Well EM, eh.......well let's see. It's to do with something called hormones. It's just one of the many ways boys and girls are different."
"And boys get hairy too, don't they?"
"Yes. Yes, they do."
"But girls get hairy too, don't they?"
"Well, yes. But boys generally get more hairy than girls."
"But girls get hair down there on their pee pees, right?"
"Ahem. Yes, EM. Both boys and girls get hair there."
"But I can cut it. Right?"
"Well, yes. I suppose you can. Some girls do, I guess."
"Oh good! Because I don't want it hanging down to my knees!"