State laws vary on this -- some specifically prohibit discrimating against children, other don't. If you are from California, I believe (not completely sure) that California prohibits discriminating against children.
Some steps that innkeepers take on this:
1. Limit occupancy to two per room; most parents want the kids to sleep in the same room, and don't want to pay for a second room for the kid(s).
2. Noting that the inn is appropriate and is designed for adults, with little to entertain/occupy kids.
Hope this helps!
Sandy
Sandy Soule
BedandBreakfast.com
Sandy@BedandBreakfast.com