I don't know about healing skin cancer itself, but I've had great luck using Oregano Oil to burn off irregular brown spots on myself. I'm still experimenting, but so far, so good.
You have to apply the Oregano Oil (100% pure) to the brown spot with a Q-Tip, and let it sit on the spot as long as possible. It will burn. The spot should turn hard and crusty, and then turn into a raw looking red spot.
I follow this up with applying Colloidal Silver
about 5 times a day. This begins the healing very quickly. There appears to be zero scarring.
I was very brave, because I did this on my face. It seems to work much better with the raised spots than the brown patches, but I have had results getting rid of both.
If it were my child, I'd see a dermatologist (just to get a diagnosis), especially if it's causing Mom any anxiety. But many of these spots are very benign, and the dermatologist will just suggest burning them with acid anyway.