What would you do if this were your child?

This weekend while I was in a store, I heard a little girl screaming and crying. It happens. I get that. But this went on for at least 15 mins. 

When I was ready to check out, the child (who had to be at least 4 or 5) was stretched out across the floor STILL screaming and crying. I had to step over her to get to the counter.

Her parents were trying to ignore her. The only thing her mom said was "It was past naptime". 

I'm just curious about how other parents would have handled the situation.