Thanks for everyone's input. The courts are owned by the school district and are free to the public after 4:30 during the school year. They have no policy against using the courts for lessons but they are first come, first serve but there are plenty to go around.
I've checked into other courts and they are either very scruffy or belong to neighborhood HOA's that I don't belong to.
The group is very small (4 kids total) and are all under 7 years old. I am accepting a small fee ($50/month for biweekly lessons) just to help us use better training equipment. It's almost more like a co-op lessons as I'll be using all the funds to pay for the training. I'm hoping to have enough for a ball machine to use with the kids when they're a bit older, so it is definately not really a "for profit" endevour.
I appreciate your input.