I can't say whether this is typical or not, but all efforts I made to encourage the kittens onto food failed miserably. Finally, I gave up. Two days later, I woke up and they all were chomping on mommy's always-available dry food.
I would say, just give mommy a little can of wet cat food where the kittens can see her, and make sure there is dry food out, and they'll figure it out on their own. Just be prepared, because as soon as they start eating on their own, they start pooping!