OMG this is awful. I freaking HATE to hear of kids ganging up on others or one child singled out by bullies. I had a similar problem. Nasty new neighbors moved in and got chummy with the neighborhood bully. They then decide to single my kid out and made our lives hell for almost two years. The parents also couldn't believe their little angels would do anything so mean and were useless. What was even worse was they would enlist others in their nastiness. It finally stopped when I drove over to where the bully was playing (we're talking middle school age kids here) and tore him a new one, complete with profanities and threats of beatings by paid thugs. The bullshit stopped after that. The kid's parents knocked on my door and wanted to know why I would do such a thing. I freely admitted everything but the threats, and it was my word against the little creep's. I also told then THEY were to blame because they failed to discipline their son.
IMO, you did the right thing. Minimize contact between your kid and theirs, and I wouldn't stop there. Inform the police, and definitely inform the school, especially if the bullying is physical or there are threats. Because of personal liability (think Columbine), most schools take a dim view of bullying. Good luck.
I've had to take up for my kids with similar stuff. With lazy parents who don't care. Tell your kid to tell you the next time they pick on them. And go ask the kids "Why are you saying this?" and then ask the kids "What would you do if someone picked on you for being such a mean little brat that picks on other kids?"
AMEN.THE PARENTS OF THESE KIDS ARE THE PROBLEM., Cowards JUST GOES TO SHOW YOU THAT ANY MORON CAN BE A PARENT. To do nothing about it says it all .stay away from them they are nothing but hateful people you don't want your children to be infected with this hate. good luck /God Bless/