These are all good suggestions, but a lot of the places mentioned are kind of difficult for children and not usually fast fishing. If your son just wants to catch fish, I'd consider white bass fishing where a stream enters Utah Lake. (I haven't been out in a week but I bet you can still catch fish. In line spinners are a good choice.) Also, in Utah the fastest trout fishing is often for stocked trout, usually in urban (or nearby) ponds. I haven't fished any near salt lake, but the highly rated ponds on the utah state fishing report map are often not too far from the truth.
https://dwrapps.utah.gov/fishing/fStart
One other thing: I think the fastest small stream action is usually in the Uintas, though that won't be till later in the summer. I'm not an expert, but feel free to PM me when it comes around if you're looking for a spot to try.
https://dwrapps.utah.gov/fishing/fStart
One other thing: I think the fastest small stream action is usually in the Uintas, though that won't be till later in the summer. I'm not an expert, but feel free to PM me when it comes around if you're looking for a spot to try.