I wouldn't be attacking the carers here. Bullying isn't something IMO a 3 y.o. can even do. If you define bullying... a 3 y.o. isn't even that aware. They might be enabled to behave in a certain way, but its not the same as waiting behind the bushes to beat the geeky kid up KWIM?

I know how you feel don't get me wrong, I've been there. But there are things YOU can do that don't even involve the kinder at all. Why not talk to the other child's mother and see about making a play date... have the mum over for coffee but get down on their level and play. Give your child the tools to stand up for himself. We taught DD that if someone couldn't respect her space and an adult didn't respect her by intervening when asked then she could yell as loud as she wanted for the offending child to stop/leave her alone/go away. We even roll played it. And I still help her with the social tools at 7, to stick up for herself, say what needs to be said and build her own self confidence. We can't be there to stop everything but we can provide them with the tools so they can do it without us. But you'd be surprised but often a toddler that appears to be a bully, doesn't have the tools themselves, is just excited or really wants to play and is actually pretty sensitive and it displays as anger or nastiness.

One great word of advice my DD's old principal told me is this Bully's are not lurking around every corner... an altercation between two children even when there is a struggle of authority is NOT bullying. But children CAN be emotionally affected even by these altercations. So its ALL our jobs to prevent that situation from becoming a bullying situation.