Choo-choo

Choo-choo=a train - used by children or when speaking to children
 

Goody-goody 

someone who tries hard to be very good and helpful in order to please their parents, teachers etc - used
especially by children to show disapproval 

No-no 

something that you must not do because it is considered to be unacceptable behaviour
Colouring your hair was a no-no at that time 

yadda yadda yadda= blah, blah, blah 

 said when you do not want to give a lot of detailed information, because it is boring or because the person you are talking to already knows it 

wee-wee 

to pass water from your body - used by or to children = urinate