That's drawing a pretty long bow. If there was an arms dump involved that would be very relevant info that you'd really hope would be included in the article.
I don't know how the editor let this slip by.
A small shipping container on the jetty had been destroyed by an Israeli missile the day before, based on intelligence indicating that it might have been used by Hamas naval commandos to store weapons.
This is where the "children were playing".
I think the list of places in the Gaza strip that 'might have been used by Hamas to store weapons' is exceedingly long. The thing was already destroyed, and as the next sentence says:
Some analysts have questioned that intelligence, however, since there were no secondary explosions after the structure was hit and journalists staying in nearby hotels reported that no militants had been seen around the jetty that week.
Again there are many thinks things we don't know about the situation, but the extermination of three young boys fleeing the scene after their friend had been killed seems pretty clear.
Unless I missed it, this is supposed to be the alarming aspect of the incident. They were probably playing hopscotch over at the arms dump. We know Hamas wouldn't encourage kids to risk their lives.