Bluegills hang out around pretty much anything but anywhere that there will be aquatic and terrestrial insects is going to be your best bet, docks, weeds, brushpiles, coves with mud bottoms all seem to hold bluegill.
As for bait and tackle, get a light spinning rod or spincast combo 4 or 6 pound line is probably ideal but the 10lb stuff that's on most spincast combos will work. Keep it simple, but some nightcrawlers or crickets or get some Gulp crickets or crawlers. Put those on a small aberdeen hook, a size 8 is about right, pinch on a small split shot or two, set it under a small spring bobber not a round one, the pole shaped ones are easier for fish to pull under so they're less likely to let go after they eat the bait. Make it about him catching fish. Take an ultralight and toss a little grub or something if you want to fish but him catching fish should be the most important. Take plenty of snacks and drinks and when he wants to go, go. Don't get frustrated if he gets impatient and don't get mad if he keeps getting tangled or snagged. You want to make sure it's a good experience for him because you're fishing for a big one here, a potential life long fishing partner and a way to connect with your son.
This is what my dad did with me when I was little and to this day if we can't talk about anything else we can always talk about fishing.