The kid was a whole lot easier to understand than the rapid fire speech of the ATC's.
Probably pretty harmless - the kid would have been saying what his father told him to, and I believe the pilots were told in advance and they seemed to by OK with it, even enjoying it.
So, while the ATC no doubt will be forced to fall on his sword, overall a bit of harmless fun.
My only slight concern would be what if things suddenly turned pear shaped in the tower, for whatever emergency. Then you have to worry about getting the kid out of the way. But that's getting pretty picky I guess - given there are often visitors to the tower.
BTW, off-topic, but the other day we visited both the YMMB and YMEN towers, flying in from YLIL. Great experience - if you ever get the opportunity do it. Nice to see things from the other side of the mike.