DS1 is a super chilled toddler and is also used to his wild little brother and many cousins. There have been quite a few incidents, where another child has hit DS1, pulled his hair or sat on the same toy vehicle eventually toppling him off. In all instances the parents have been present and are very non-reactive because DS1 is not loudly crying or complaining. Instead he just keeps saying, " please stop" or "move please".
In all cases I have said to the child (hinting at the parent), "Be careful X," or "You can have a turn in 2 minutes," and so on. This clearly isn't working as the parents are not bothered and eventually DS1 gets hurt, but still does not complain. He just finds his own space away from the child.
I'm not sure how to deal with this. What do I say to the parents/child without coming across as being rude. I don't wants my DS1 to learn that his mother is not there to protect him.