How should I approach a parent when I think a child's safety is in jeopardy?

Just a couple of week's ago I rented a movie from Blockbuster. It was at night and after returning to my car I saw a father walk toward the store with his two young sons (look to be about 2 or 3 yo). They had to walk from parking lot to the space where cars are driving in and out in front of store. These children were energetic and were not holding the father's hands. One child walked behind the father. The father walked, looking straight ahead. Not once did he look back at the child behind him. The little boy was running to catch up and would not have noticed if a car should suddenly pop up in his view. I'm seeing this a lot lately with young parents. I debated (to myself) on whether I should enter the store and say something or should I just drive off and mind my own business. Well, I decided that I would risk getting "cussed out" and entered the store. I approaced the dad and asked him to please hold the boys' hands, etc. He said that no car was coming,it was ok. Next time?