My 16 year old son and I dove Key Largo for the first time the last weekend of July. We dove the Spiegel Grove (twice), the Benwood, and French Reef (over a two day weekend). French Reef was no deeper than about 33 feet. We had a really nice time diving that reef, which had much to see in terms of sea life and "landscape". There are a number of other really popular reefs in Key Largo to choose from. If we had more time, we would have dove some others also, but we are from Orlando, and needed to get home after the weekend.
I did a lot of research concerning who to dive with. What I found is that there are a fair number of good choices, each with a loyal following and with good reviews. For me, since it seemed that most had reportedly very good crews, it came down to ammenities. My three final choices were Silent World, as mentioned above, Quiessance (not sure I spelled it correctly) and Keys Diver. Keys Diver won, since they have a larger boat (smoother over waves), which included a head. I drink a lot of water, and so the head mattered to me (insert the Pee in your wetsuit comment here. LOL). The others did not have a head on their smaller boat. Keys Diver was very friendly and welcoming, and I thought the crew was awesome (especially dive master Kim. She was awesome to talk to).
Have Fun, and dive safe. I hope having your child as a buddy is much of a blast for you, as it is for me.