Maybe if you started out in a casual conversation asking the dad....”Do you think the boys tromping on those plants will hurt them over the years?” See how he responds??? Then, if they get tromped and hurt, you might come back and say....”I’m worried about my plants dying....” JMHO (I LOVE MY PLANTS, TOO!)
IMHO, this is just one of those things that happen when you have neighbors, no big whoop. I would just causally say something when it happens, like, please be careful when you go in there. Nothing to worry too much about.