It does look like poison ivy, especially the small blisters. Go to the store and get some calamine lotion to put on it. And he needs a bath to get rid of the poison ivy oil to keep him from rubbing the oil onto new areas.
If you get it near the eyes, a doc will give you steroids.
We once mentioned to our pediatrician that we were sort of embarrassed about the number of bruises our kids had. And the doc said he would be more concerned if the kids didn’t have some bruises. And they weren’t autistic, they were normal kids.
Poison ivy is very hard to prevent. In fact, if some idiot burns poison ivy a mile down the road, you can catch it from the air.
Simple test.....if it itches, it's poison ivy, if he doesn't touch it and acts painful when touched, it's a burn. My bet is he constantly scratches and spreads the agent.
Look at the pics and they show a large blister in the middle with smaller ones on the fringes. That looks EXACTLY like poison ivy.
If he doesn't respond to verbal comands, it will be almost imposible to stop him from touching them and spreading the agent, even to his eyes( and scrotum). Then you really have a mess.
If it's a burn, well, keep them covered and try not to bust the blisters for as long as posible. Then apply antibiotic cream.