My 14yr. old is a Jr. OW diver (about 20 dives) and his brother 12, will be one early in the spring. I bought the 14yr. old a Poseidon BeSea W50 because it will fit anyone from XXS to XXL (the torso length is adjustable in addition to all the standard adjustments, plus the rig is very modular). He might wear it out or tire of it, but he'll never outgrow it (he grew 2" last year.)
His reg is a Tri-metal (XS Scuba). It breathes VERY nice, as nice as my USD Legend LX.
As for kid-friendly destinations, I'm having similar issues (PLUS, my wife doesn't dive). Pretty much anywhere with beach accessible diving and calm water boat diving at moderate depths (65' or less) is what we've looked at for our son. We hope to head to Grand Cayman for spring break. I've also been told by a co-worker that CoCoView (Honduras) is a perfect site. Not a lot for the nondivers, but beach dive leads to a wall and a lot of the boat dives will drop you off along the wall to let you migrate back to the resort w/o worrying about the boat. I was told that it made for some very leisurely, low stress diving.
He said he takes his daughter (diving since 12) all the time because the shallow dives at the entry and the "wreck" are as good as any he's been on (and he's been diving a long time.)
Our LDS plans trips that are teen friendly, since they certify a lot of them. But, I wish more resorts would cater to younger divers and their families.