It is actually pretty simple. He needs to ask the TSO to hand screen the cameras because they contain undeveloped film. The TSA policy requires TSOs to hand-screen undeveloped film when requested by a passenger. The TSO will likely ask what speed the film is and suggest that passing it through "this one time" will not harm the film, but if you son politely repeats the request for a hand-scan it should be no problem.

Many of the disposable cameras actually use higher speed film than not (400 or even 800) and that makes them more prone to damage from the x-ray machines.

The hand screening is just ETD swabbing of the case and should only take a few seconds extra.