Self-harm in toddlers can be hard to pin down.
It's very common with autistic children and children with sensory disorders -- they can block out overload or frustration with something easy to do that shuts out whatever they're having trouble ignoring. If you already suspect autism or a sensory disorder for other reasons, I'd look doubly hard at the possibility now. If not, then there are other causes to consider:
Some toddlers self-harm simply because it's something they can control in a world that is almost completely out of their control. The best way to discover if this is the case is to increase opportunities for your child to be in control of things and see if the self-harm abates. Some ways to do this are:
- Encouraging the child to make simple either/or choices as part of your everyday routines, such as picking out his own clothes each day from two choices you have offered
- Making sure that you and everyone in your family is very consistent in how you react to your toddler's behavior -- if he knows that behavior X always results in an immediate time out and behavior Y gets consistent praise, he feels like he knows how his world works, but if X is tolerated without reaction until you get really annoyed and blow up, he has no idea what happened and feels like it was just random, which is very frightening.
- Making sure you provide your toddler with a stable routine, so he/she can predict what is happening next, or how common events (a haircut, cleaning his room, meal time, etc.) will work.
Some toddlers self-harm because they don't know how to handle feelings of frustration or anger. Helping your child communicate more effectively (absolutely teach and use sign language if verbal communication is difficult for him!), and helping him learn what is appropriate to do to vent those feelings will help stop the self-harm if this is the case.
Some toddlers self-harm because they've learned that it gets really intense reactions from grown-ups.
Finally, some toddlers self-harm as the result of abuse. The answer is to get the abuser out of the child's life immediately and permanently, and understand that it will take time for the child to adjust to his new world and phase out the self-harm.
There may be other reasons, but these are all the ones I've dealt with. Whatever the cause, cutting the fingernails only helps so much; a child with even very short nails can often draw blood anyway, and if not there's always head banging, hair-rending and so on.
While you work on figuring out and dealing with the cause, try restraining your child when he begins to self-harm. Do it calmly, and don't give any huge reaction or try to reason with the child about it. At least in my experience, self-harm is a self-reinforcing behavior -- the more you allow him to do it, the more he will want to do it.