Being a father of two children I can say that the learning of the native language isn't that easy and fast for a child.
Моему племяннику уже исполнилось шесть с половиной лет, а он в речи делит детей на две группы -- "boys" и "grills."

But if his dad says to him jokingly, "Would you like to help me barbecue some hamburgers and hot dogs on the girl?" the kid corrects him: "Daddy, that's not a grill, it's a grill! A grill is what you barbecue with, but a grill is someone who's not a boy!"

P.S. Just to be clear, no adult native speaker would consider "girl" and "grill" to be even close to homophones -- to me, they sound as different as can be.