You would have to pay a fee to downgrade your reservation to one less person, I believe it's $50.00. I've done lots of single mom trips, but I only have 1 kid so I can't help you with that. I can only say that I wouldn't have let a 5 or 7 year old ride anything alone. You just don't know what could happen in the middle of the ride, they might get scared, etc. There are plenty of rides the 3 of you can do together. Good luck on your trip - it's too bad it's not the one you had planned but you will still have fun!