She's immature and infantile. (best Creole translation)

infantile → entatad (en-tah-tahd), annanfans (uh-nuh-fuhs)

She's immature (infantile).
Li entatad.
Li annanfans.

You are so childlish!
Ou s'on entatad!
Ou annanfans!

"entatad" and "annanfans" can also translate: half-witted, foolish, unintelligent, bird-brained, nutty, etc...