bite on my son skin
I'm so sorry for you son, this looks painful!
Unfortunately, we don't have the medical training or know-how to identify this. I'm not even sure it is a spider bite, or if it might be an insect of some sort.
My recommendation would be to share this with his pediatrician if possible. If the symptoms get worse, I would consider a visit to a minor emergency clinic.
I apologize for not being able to help you. If you find an insect or spider, we'll do our best to identify it for you.