Honestly, if kids are going to be around an animal I do NOT want them to touch, I put the animal in a room that has a door that can be shut. Out of sight...out of mind.
Kids are kids and not every kid at the same age is responsible or mature(that's why they're kids and not adults, heck even some adults don't listen too well). I work with school age children and in a classroom the behaviors from one to another in the same age group are vastly different.
I personally, would not take a small fragile puppy where there was going to be kids. I think your own kids are different from someone elses(even a close relative). Kids also have very short attention spans. I'm sorry it was so stressful. I'm sure you were soooo glad to get back in that car! There was a thread about a little girl who sprayed a mom and puppies with something because they smelled(pooped) and it killed the puppies. Kids don't think things through. Even teenagers make stupid decisions so you can't expect a 6 and 8 year old to be mature enough to listen if they aren't capable. Each kid is different.
Just remember next time, you can't control someone elses actions...only your own(keep the puppy out of the line of fire