1. Where is the little boys' room?
2. Where is the little girls' room?
[Is the person looking for the restroom for little boys/girls or for all male/female persons?]
male and female restrooms. The age of the person doesn't matter. It's a "cute" way to ask, "Where is the toilet?" It's thought to be "nicer" than to say, "I need to use a toilet. Where is it?"
I haven't heard anyone use the term "little girls room" or "little boys room."
It's best to ask, "Where is the rest room?" or "Where are the toilets?"