The hugging is just fine. If a parent thinks you shouldn't be hugging their kid, then they shouldn't send them for playdates - shows distrust for you, and I actually would not want to have their child over if they felt that way...
The problem I have with how this all transpired is that you promised not to tell the mommy, and you did. NEVER promise not to tell the mommy, even if there are tears. You cannot keep a promise like this, and you shouldn't make a promise like this.
These kids don't understand the meaning of the F word. They just know it's naughty, and they are feeling their oats. It's up to you to say "We don't say or spell that word. Ever. Do you understand me?" Then you tell them that if it happens again, you will send them ALL home immediately. No more discussion. Of course, you call the parents and ask them to tell their kids why they cannot say the F word.
Instead of giving separate children the 3rd degree, have the discussion with the group and be STERN about it. They will try to say "Not me, it was him" and you ignore that and continue with the whole thing.
The thing is, sometimes you have to act like you're the Army. If one person screws up, everyone gets in trouble. They will stop each other from misbehaving if they all pay the price for things they aren't supposed to do.
Just to let you know, when my kids asked me what the F word meant, I said to them "It's the WORST word in the history of bad words. The absolute worst!" Their eyes got really big. (My son did spell it - he knew not to say it, but just didn't know why...) Fast forward a month later, I was standing on the sidelines of the soccer field with another mom, and my son said to her children in front of us "Did you know that the F word (he spelled it) is the WORST word in the history of bad words?" I thought I would die. The other mom was as shocked as me, but understood that little kids say all kinds of things. And yes, my son and I had another talk...
Dawn