For the float fishing, if you use a dink float that slides on the line and those bobber stops, you can adjust your depth. Your lead (assuming your using lead shot or pencil weights) should be bumping the bottom every now and then. If you're presentation is not in the bottom 1/4 of the water column then you got no chance. Otherwise, it's not too complicated and definitely something you or your kid can google or youtube for more details.
If he gets bored with float fishing, try pink spinners and pink jigs. Same concept applies, be in the bottom 1/4 of the water column, but it's a bit more forgiving since there's some attractive action to the lure so even if you're only in the bottom 1/2, you still stand a chance of getting a fish interested. But it's definitely important to put your presentation in their face.
Also spend some time looking over the bridge / scouting the fish and find out where the fish are lining up. Only fish where the fish are stacking up... goes without saying but it's amazing how many people fish dead water for hours, especially at the popular spots like the bridge. If you can't get your way into a spot where the fish are, then move on and find a new spot.
Those that just "fish" don't usually catch.
Those that spend a bit of time "hunting" tend to catch more often.