Neighborhood 'friend'

We have a neighborhood boy (9yrs) that comes over to play with one of my triplets (6/m) a few times per week. We live in a cul-de-sac and sometimes this boy will play either kickball/baseball in it with his brother (12) and some other neighborhood kids that are all between 9-13yrs. My son is very social and loves hanging out with older kids.Yesterday my son wanted me to ask them if he could play. I said that he could go ask them himself. He replied "they will just say no and that I'm not allowed to watch" I encouraged him to try and I guess when he walked outside he told me the 'friend' said "let's throw the ball at (sons) head"My son said "I heard that" and they said "we don't care"This isn't a isolated incident and unless a parents out there they are like this.Do I say something to neighbor kid when he comes over next? His mom is pretty awesome and I thought about texting her about it but I don't want to make things worse for my son.It's really hard for me not to get involved because I grew up with a neighbor that terrorized me and my brother. I also don't want to blow things out of proportion because I have issues.I just honestly want my son to learn to stand up for himself but they are all older and that is very intimidating.How to handle this? Advice? via /r/Parenting http://ift.tt/2trLTu3