My older DD turns 8 next week and also looks after her baby sister. It's the millions of other kids we don't know packed into the tiny fast food play area I worry about. Those places can be crazy. The 16 month old hasn't started following her big sis and friends around yet. I'm sure that will start soon. That's great your older ones help out. It makes it much easier.
I know and they are so rough. They will push the baby out of the way to get to slide or stairs or whatever they are trying to get to.