infantile

adjective
in·​fan·​tile | \ ˈin-fən-ˌtī(-ə)l How to pronounce infantile (audio) , -tᵊl, -ˌtēl, -(ˌ)til\

Definition of infantile

1 : of or relating to infants or infancy
2 : suitable to or characteristic of an infant especially : very immature infantile humor