If I visited my friend and her 3 year old grandchildren in the Netherlands, they loved nothing more than giggle about piss and poo. Our eldest has the same age, but in those days I never heard him say anything about the subject. So I thought it was a Dutch thing.
At the moment the youngest is 3. And guess what? He loves nothing more than giggle about piss and poo. Their favorite bedtime story is Todos hacemos pipí (All pee) from Frédérique Loew. It’s about the pee of all kinds of animals. Giraffe, chameleon, zebra, monster, dragon. Funny.