kids: DISCLAIMER: Free advice is often worth what you paid for it, so don't complain if you aren't satisfied with the product.
Disclaimer aside, here goes: Don't get in the middle of disputes between kids. Don't let very much emotion get in the way. Kids, especially boys, can hate each other for a few weeks and be best buds for years after. Or they can go back and forth. If the adults get involved and get angry, they rarely get over it with anywhere near the ease that kids do. The kids are back to being great friends and the parents feel awkward around each other.
The great majority of situations call for parents being supportive, helping their kids understand where other kids may be coming from and staying out of the way to let them resolve it themselves. I'm not talking about serious bullying or violence. Those are separate issues.