I wanted to ask my son why he doesn't eat enough.

Why do you eat so little? <------ Is it right in English?  yes it's ok to use this expression


How to say to kids ..

Do you want to pee? <--- is small thig.


??????? < ------ when it is big? How to say?  / Do you want to go to the toilet? 

Hi Yanna,

You can also use the expression "I need to do number one” means I need to pee.