Where have you lot been???
Ever since I can remember, toy guns, swords or other weapons have had to be carried in hold baggage - never in the cabin. Quite apart from the fact that some toy guns are very realistic, having been successfuly used in past hijackings and bank hold-ups (I recall a plastic toy 7.62 mm Self-Loading Rifle 100% accurate down to the last rivet that I confiscated from an 8 year old in Northern Ireland when I was in the employ of Her Majesty as a regular soldier), the noisy play often associated with such toys could cause shock and irritation to passengers and crew alike.
It is somewhat ironic that the Daily Mail reported this story on the page before another article where two young boys had terrorised a neighbourhood, so I'm afraid the question of youth doesn't really hold water!