Right, thats completely logical. I can teach you to kick and punch, teach you how to use the body weapons you take with you anywhere, but I question the students judgement enough that I won't teach them a weapon. Apparently it takes a genius to figure out how to swing a stick....
I don't think it's the technical aspect which is the problem, but the... um, behavioral part. The instructor doesn't want the kids using each other as uke, willingly or (more likely) unwillingly, when a force multiplier like a six-foot pole is involved. It's bad if a child decides to check out his current skill set on a friend (or otherwise); it's way worse if he does it with with something, like a bo, that allows him to translate a moderately fast arm torque into a really scary angular velocity.
There's something to this caution... I keep telling the kids in my TKD classes, don't do this stuff to each other. Don't. Don't. Don't... and I am always seeing them doing it anyway, during the water breaks. And a lot of them are around this little boy's age, or just a bit older...