You're putting a lot of money into a bike that is too big for your son with a cracked headtube.

Here is a 54cm Specialized Allez frame with misc parts for $80. Other frames or bikes that could be rebuilt will show up on Craigslist from time to time.

As far as the hose clamp... I don't know. It would seem like it would take quite a bit to rip the headset out of the side of the top tube. But, at the same time, you wouldn't want to compromise the steering. And, it just plain looks funky.

I wonder if the headset originally was too big for the head tube causing the cracks.