I am just gutted... my ds1 has ended up in a pre-primary class with bullies.... again!

Background - he went to a diff kindy last year, was in a split kindy/pre-primary class. Majority of the class were pre-primarys and quite a few boys. A few decided they didn't like my boy. I know he's not a perfect angel but he had his chair pulled out when he was going to sit down, tripped over, rocks thrown at him in the playground, they would ask him to play then run away laughing, sit on him so he couldn't get up etc... yes, I brought it up with the teacher but got fobbed off. Anyway..... so we moved to the local primary school for pre-primary.

So far they've had a staggered start, half the class a couple of days, the other half the other days, make sense? The group he's in has been fantastic! The teacher has even commented how well they all get along, boys and girls, and how great it is. One of my close girlfriends has her son in the other group, man, the stuff that's come home already from 3 days at school is amazing! There are 2 foster brothers in this group, so far they've tripped him up in class, slapped him in the mouth and threatened to punch her boy at playtime!

Why??? why are kids like this???? It's just not fair and it sucks! My kid does not bully, he plays with everyone. What can I do to help the situation? I already said to the teacher the other day how happy he's been and how he was bullied last year, this was before I knew what was going on.

I'm tempted to tell him that if anyone thumps him he can feel free to thump them back but I know that's not the answer! Anyone had any experience and can help me with this? I'm freaking out that this year is going to be like last and he's going to hate going to school. He was so happy the first day, the first thing he said to me was 'mum, ALL the kids are nice here'! Now his little world is going to be shattered.

For gods sake, these kids are 5yrs old!!!!!!!!!!