I will admit to having a lot of hangups with naked human bodies. I would personally be very uncomfortable with myself or my children seeing the crane or the lawn mower, but some of his stuff was really nice. Even if I don't like it, unless you had simulated sex acts on the walls, I wouldn't have a problem with it. If you did have true porn on your walls, you would not be watching my child. They asked you to watch their son, they should have been bringing you brownies!
I did like hte ones with the pregnant bellies, particular the stork. I may just have to get a print of that one. If it's covered by a bikini I'm not fond of it, but the ones that were just stomachs were neat.