No kids of my own but I have nieces and nephews who used to come over with homework because their parents worked and got home really late. (Until one moved to another country, and the others to a different place in the city. And in special cases, the other cousins would still drop by.)

I normally check the homework notebook containing a list of what they'd need to do. I'd ask him/her if they understand the lesson -usually having them explain to me what was going on. If I feel like they're okay with the lesson, I'd let them go on with the homework and just have them let me check it afterwards.

If they don't seem to grasp it, I usually would try to explain the work before having them do it. This would sometimes take a while, however.

As for projects, I just usually kept an eye on them but I wouldn't do the work.