we have been really lucky and haven't had much of this, but I think you should talk to the people at childcare and see if they ca shed any light on why this is happening. it sounds like he is having nightmares, and also that if he doesn't hold on tight to everything he want's someone will take it?

you are definetly doing the right thing by ignoring the tantrums as paying attention may reinforce.

I don't have any good suggestions though, except practicing sharing at home??