Kitten pot bellies

Hello, I am the one who adopted the stray cat that wound up being pregnant with 9 kittens. I have noticed that a couple of the kittens are starting to get pot bellies...should I be concerned about this? I hold them up to the mother, and she licks them like she should. Does this mean that they might be sick or are getting more food than the others?

They all seem to be pretty energetic unless they are sleeping, of course. Also, I noticed they kind of shake when they roam around the box. Is that normal for a 4 day old kitten?

4 day old kittens can's walk, so they would be unsteady on their feet. I would not worry too much about the bellies. But chances are with mom being a stray and probably not wormed before pregnant, the kittens will have roundworms. When you get their first shots at 7-8 weeks old, I'm sure the vet will worm them. Be prepared for a little extra expense.