My first thought when you mentioned having 2 autistic children was also parasites.
The person who posted the video above gave you a good start.
Kerri Rivera is up to 86 autism recoveries now. It's amazing. What is also amazing is that while treating the children, parents and other family members are also doing a parasite protocol and finding they have them also.
To answer your question, a parasite infection can have many symptoms, or just a few. Dark circles and hair thinning can definately be indicative of a parasite infection.
Hope you get it figured out and definately watch that video!