I was in HDU and my parents came to visit. I was pretty out of it; I don't think that they stayed long, but just wanted to see with their own eyes that I was ok. It will be different for kids - sorry if I've missed it, but how old are they? I'd play it by ear - some people come through and are in little pain, I remember being in masses amount of pain! I was also attached to all sorts of equipment (oxygen, heart monitor, blood pressure, flow trons as I didn't have stockings, erm, plusox, and IV fluids) which may scare children and I also had a drain in wound. I didn't actually know that the drain was there until the next morning though lol!
As for the eating, someone posted a video on Youtube that I've seen.
I don't know how accurate it is, but it's my understanding of not drinking straight after eating. However, I do do it sometimes, if I'm desperate for a drink or need to wash something down that feels a bit stuck.