Eddie,

The pink salmon in that system are all wild and lot's of them get snagged by "fishermen" looking for the kings and silvers. There is also the issue of the crappy visibility in both of those rivers at that time, which can make getting them to legitimately bite difficult.

In the relatively clear water of the Snohomish and Skagit, the pinks bite readily and IMO, it would be easier for your son to catch one.