It also would have far worse visibility than a Ford Explorer.
That said, I don't think it is an argument for whether he should be "allowed" to have the truck or not. If there was evidence that people with large truck always hurt kids, perhaps; but I don't think that evidence exists.
As for visibility, I think that probably cancels out with a responsible driver. The fact that it's harder to drive will engender additional caution, for probably no major net change in danger, assuming he can avoid getting so used to the thing that he gets sloppy.
I'll also bet that his fire truck can stop better than you think, especially if he has left the ~500 gallon water tank empty.
/sarcasm
On the other hand a new tender (or water pumper) CAN stop on a dime, as its brakes are based on it carrying three to four thousand gallons of water, so when it is empty...