My ds2 is 20m old. He has a habit of biting his brother and sister when he doesn't get his own way. Always over toys, e.g. if they are playing with a toy he wants, he tries to grab it, then tries to bite them (and usually does). This happens about 10 times a day and I have tried everything, sitting him on the naughty step / taking the toy away / ignoring it and giving the offended sibling a cuddle.
For the last ten days or so he has started biting his own arm too, and has ended up with a lump on each of his forearms from biting constantly in the same place.
I really don't know what to do about this, I've tried putting him in long-sleeved tops and saying "no" which stops him but then he goes back to it.