Was about to say, DD2 was under a year (although not by much) and now at a year and a half still giggles and says "poop poop!" and then giggles again.
DD1 is 4 and does not find them funny anymore, but does think calling someone a "poo poo head" is just about the funniest thing ever (until I remind her that she loses a bedtime story if I hear her calling people that).