My son isn't here yet, but my friend has a 9 year old and his little brother found the first baby tooth the older one lost. The mom likes to hold on to stuff like that because it's memorable to her. Anyway, the 9 year old comes up and says "mom we have to talk" and showed him the tooth. The mom goes "that's because the tooth fairy lets the parents keep the first and last tooth lost"

Which yes he's old enough to know the tooth fairy isn't real, he probably already does, but she wants to keep giving him money and he's kinda a loud mouth right now and would ruin it for his little brother.