How do you say sleeping in french?

To sleep is dormir.

French does not have a perfect equivalent of "-ing" verbs in English. Here are some examples to show the possible translations:

Be quiet, the baby is sleeping. -- Parlez doucement, le bébé dort.

I should stop sleeping all day. -- Je devrais éviter de dormir toute la journée.

Sleeping Beauty -- La Belle au bois dormant (in modern language: la belle dormant dans le bois)

One could also say: J'ai fait le grand matin.

Literally translated this means "I made the big morning" but really it means "I slept in"