What should i do! with my puppy!!?

Hi all, so i have a 5week old Chihuahua, yes i know hes to young to be from his mum but that was the owners choice not mine, hes cute and all but hes starting to have these little fits, growling, barking, biting, all kinda stuff, i know its a puppy thing but will he grow out of it?Iv given him toys and all sorts but he likes the human flesh bit better then his toys. hes a pretty vicious little thing, im worryed cause my cousins are little and hes got sharpe little teeth and i don't want him to bit them!! is there anything i can do to get him out of this Habit!!