I think a Flying 15 would be a perfect boat for you and your son. I had one and it still planed with three up, all adults.
Designed by Uffa Fox, they were "the first of the planing keelers". You can anchor them close enough to the beach so that you can wade ashore with the Esky and BBQ or you can drag a Clark Rubber 6 ft inflatable up on the back deck.
Barry and I used to refer to ours as the "geriatric's dinghy". Very hard to capsize one but the rules require you have flotation in the bow and the stern. Bean bags do that job very well and give you something to sleep on if you want to camp overnight. Add a boom tent and you are made. Terrific yacht if you want to graduate to a larger keel yacht later on.
I think your 8 yo son would grow into it and by the time he is 12 he will be asking you to just tow it to the boat ramp and come back a few hours later while he takes the girls for a sail.

The Flying 15 is a chick magnet.