In my opinion here's the secret to fun times while warm water fly fishing (regardless of what you may have read in magazines or seen on TV shows): the fish don't have to be monster sized in order for you to have a blast catching them. Hooking into 9" small mouth bass or even sunfish 4" across can give you so much sport you'll be grinning from ear to ear. This is especially true if there are a lot of fish around & you adjust your tackle for the situation. These fish are are much more abundant in most places than the cold water fish, like trout for example, so they're a great way to introduce a youngster, or any beginner, to fly fishing.
In choosing a fly rod, I look for a slower rod. You don't necessarily have to go with a two weight rod to make a 5" bluegill feel like a shark. A 6 wt rod can do that - assuming its got a lot of flex & bend to it. This fishing is a great opportunity for an old fiberglass rod or that lower-priced production bamboo rod that hasn't come out of its tubes in years. I like using older glass fly rods for this type of fishing, but that's just for personal & sentimental reasons. No matter what rod you choose, look for one that bends easily. You might have to adjust your casting for the slower rod, but so what? Why be in a hurry? Just leave your high-end dry fly rod at home. You won't need it.
You also won't be needing any expensive or fancy fly line or reel either. A simple single action reel to hold the line will do fine. It doesn't have to be the smoothest reel you own, as you won't be using it much. You'll land most of these fish without putting them on the reel.
As for fly lines, again you don't need anything too fancy. In fact your line is going to be getting in the mud & the green nastiness floating in the water so maybe keep the expensive line you use for trout at home on your nicer reel. Even a level floating line will work for this, as you won't be casting extremely far.
Choosing a leader for this fishing is easy. Yes, you could put on a tapered leader (knot-less or otherwise) or you could just use about 4 to 6 feet of level mono-filament of around 6 lb test. Careful presentations & long, delicate casts are not going to be in store when you're casting poppers or streamers with a ton of hair &/or fur on them. The leader is going to take the brunt of the abuse & a spool of plain mono is cheaper than tapered leaders - & you will be going through a lot of leader material in the waters that these fish sometimes call home.
When it comes to deciding which flies to bring along, I like to carry an assortment of poppers in all colors. I also wouldn't be without woolly worms, buggers, & some mudler minnows either. Color can be very important to these fish on some days while at other times it seems to make very little difference - at least in my experience. To be safe I like to have a bunch of different colored flies on hand as well as a few flies with some flash & shine tied into them.
It's most likely going to be hot & muggy when you're going after these fish so go lightly. Maybe wearing a vest filled to its maximum capacity isn't a good idea. Stay hydrated, too & don't get sun burned.......all those things your Mother told you about playing outside in the summer.
The fish like I'm talking about here live just about everywhere. Most of us have access to them. Not only will they be in some of the places where you were catching trout this spring, you'll also find them in ponds, lakes, streams, & rivers, too. Maybe you don't think you live in close proximity to good fishing water, but I'll bet these fish are closer than you think. Does your city have a park with a pond? Do you have a golf course nearby? I'll bet if you look around you'll find a place close by where you can do some warm water fly fishing.