Eepster is right. Alopecia is the medical term for hair loss, but really doesnt point to a cause. It can be reversible or permanent.
Its great that you are going to see the dermatologist. Remember that you and your son are in control--its your choice how to treat this. The MD is a great resource, will hopefully be able to tell you what is going on, and offer you some choices in treatment. Then you can take a deep breath, and decide where to go from there.
There are lots of great provider who have non-toxic tools to help with this. I didnt see where you are, but depending on your state, you could see a naturopath (great if you find an autoimmune condition), an acupuncturist, nutritionist etc...
If you want to, you can look for the "black dot" effect--a sign of tinea where the hairs break off close to the scalp.
Here are some
pictures of what that might look like.