Actually it is an old phrase "hit themselves over the head"---- some kids do do this. My son would sit down on the floor and bang his head on the floor! Ugh. He'd be at the top of his frustration level. He had a hard time coping and self soothing. This is my son that has sensory integration disorder by the way.
These kids are very little and their ability to communicate is still quite limited along with coping strategies being almost non existent.
I'd begin, anyway, talking to them about their feelings. "Oh, you look mad!" What can we do about it. Give them a pillow to punch instead. This does two things . . . it helps them begin to build the language they will need to handle emotions that feel intense and soon enough, you can say "use your words" to get at the problem. The second thing it does is start to teach them that they can switch their behavior to something else rather than doing their first impulse. This becomes a technique that will be very useful for them down the road. That way, they will be able to have appropriate choices of ways to handle frustration, anger, sadness and choose the best option for them.
Tell them to give themselves a big hug too as deep pressure calms the nervous system.
good luck
That sounds like massive frustration to me. If you can i think that you need to get some outside help....Children do no typically hurt themselves over dissapointment.