Your son would be much happier with another chassis such as a sprint2, losi drift-r or TA05. those three cars are pretty much bombproof, would be able to handle the power from a brushless, and already have a large assortment of parts already available. The drift-r comes RTR with perhaps a better setup overall.
I can't put much faith into the esc handling a 19t motor, because even at the limit, the esc is working quite hard. any more and it might just end up eating itself.