I think it is perfectly alright for children to learn dialect BUT must teach them how to differenciate the words and when to use the right words, dont mix and match with different language. dear son has been exposed to hokkien songs too and he will say "AIIIII!!!" when he want foods. And I will ask him to say "please" "I want" or just nod his head. he cant pronounce 'please' and 'want' properly so sometimes he will just nod his head.