Is it illegal for a family business to hire their children?

[Grant]

So I don't know if there are any different rules for family run businesses, but I always noticed that some mom & pop stores seem to have their own kids as hired employees. Is there some rules where families can hire their own children if it's a family business? I think of the show Bob's Burgers as an example, yes I know it's a cartoon, but in it Bob Belcher has three kids who often, or begrudgingly help him with his restaurant. I don't think they even get paid, which brings me to my next question, do family businesses pay their children if they work too?

What rules and laws are there when it comes to hiring your own children to a family run business?