I have two views on this...
First...television should only be on when doing other things like eating, playing, etc. Never should it be on during meals nor when having family time.

Second...news is what is happening out in the real world whether we want to believe it or not. While its not good for a 7yr old to sit and watch it constantly I am sure this small bit that your child saw did not impact him...just confused him probably as it was a bit much to handle.

I think having the televisions not available for the kids to see while they are playing is best. Kids should focus on playing with the others and the play equipment supplied.
And parents should be enjoying watching their kids play. They are not kids very long after all.