I have thought about it from time to time, and been asked a few times to babysit on a regular basis for people, but I just can't. Some days it's just all I can do to take care of my own kids. Maybe if my own were very young - preschool or early elementary - or I only had one or two children - I could do it.
My job is to take care of a kid with CP before and after school (his school), I also watch his siblings. DS and I do as much school as possible while the others are in school and we do science with them because they enjoy it as well.
Last year I watched my neighbor's daughter almost everyday after school. After that experience - never again will I watch others' kids while we're doing school. You'd think after PS I should be fine, but no. We would still be trying to finish up, but I had to go pick her up, and attempt to pick up from where we left off, get her to do her homework which she constantly lied about... It was awful. This year, it will be a once in a blue moon, only if her new sitter backs out sort of thing.