How small is your child? Old enough to take any supplements? One of my staples is Borax. I read where a gal and her baby had rash allover, then started taking mild soapy borax baths and found relief.
Borax is only as toxic as salt. There are also supplements containing boron that might be helpful... That Vermizyme spray I mentioned before would be okay for kids.
Hopefully without sounding like a commercial, when I was still itching bad an equine grooming spray called MICROTEK helped a lot. I still use it on my skin and scalp/hair... It's gentle and smells a little better too ~and~ comes in a big spray bottle.
I know just how you feel when worried like crazy over your kids. Mine are older now. My daughter keeps absently touching her face and has a few pimples, but never had lesions.
Wish I had more advice ... I'm really not sure with little ones...Good luck and hang in there!