[mesmark]

I'd say let it go for now. Sometimes words kids are familiar with that have been taken over by the L1 are the hardest to fix.

In Japan, people say 'Hallo.' for 'Hello.' They write it in Japanese this way and people just think that's how they're supposed to say it. they've said it that way for so long that they can't stop even when you tell them it's wrong.

Once they get into reading and writing it should iron itself out. Hopefully they'll see there's no 'n' in pig.