English is my third language, I can speak and understand normally conversation. That hard time comes to stuff like black humor or I have to peel off extra layers to understand what it really means like the knock knock joke.

My question for the day is, if you could not be blunt to tell people off, is there any nice way to do so.

like the recent incident I had:

I was in the airport arrival area waiting to pick up my friend. I sat there listing to music and minding my own business. A lady with 4 kids show up (a boy and a girl maybe 7-8, a toddler plus a younger one in a trolley). They sat in the seats on the other side of the aisle. Not so long after, the boy started pushing the trolley like a race car; the baby in the trolley is scamming; the girl was chasing the boy yelling at him and tried to stop him but keep failing. the area is quite a congested and the boy could easier hurt someone. 

I did not do anything but just sat there and hope no one get hurt. I know it is not anyone's business how parents want to raise their kids. But what would you do? Is there any nice way to tell them off in cases like this?

Would be good to find out.

thanks and sorry about my poor grammar.

Sam:)