Give them hard questions to answer:

What would you do if Chip climbed up your curtains?
What would you do if Dale danced on your face at 4:00 in the morning?

You know the types of things...kittens are terrific but they can also be destructive and disturbing.

I always grilled prospective kitten parents hard and if they seemed hesitant...they weren't right. They needed an older cat.

Good luck to you foster mommy in finding them their perfect furrever home. I know you'll do right by them.