Try not to punish yourself. You can't make them bullet proof, and you can't be everywhere and everything all at once. The fact you feel as you do about this shows that you're a loving and caring mother. You should see some of the stuff I did to myself as a kid, and this was with a mother who thought I had a terminal illness every other day (ie. it wasn't through lack of care).

Being so young, his skin will heal and regenerate (and/or accept a graft) much more readily than an adult. The young body has a remarkable ablity to heal. By the time he's big enough to look after himself you'll probably be lucky to even see a mark. Good luck