Where's the best place around Brighton to take a 5 year old who really wants to go fishing. Not enough patience for the boat yet. Looking for some shore fishing that's easy to get in and out of in case it doesn't go well.
I think you're 100% correct to choose shore fishing over a boat, because there are usually other things on shore to explore when their attention span (maybe half an hour?) runs out on the fishing part. That was good for my kids when they were small, even though only one out of the three turned out to be a dedicated fisherman. That's reasonable odds, I suppose.
Take along some snacks and drinks, and some container to take home any "treasures" they might find.
As someone else said... Any place with bluegills or other sunfish.
A couple of months ago I took four kids (5 to 8 years old) fishing at Sawhill Ponds in Boulder. We used a fly and bobber. The kids were catching them faster than we could take them off the hook. And we didn't have to mess with worms and such. The trick is to use small flies (#16-20) and the hairier the better. Get them soaked so they sink rather than float.