No they dont they just have regular bikes with a child seat attached behind the adult seat, or tiny kids bikes with training wheels and helmets for anyone who wants them, required for the kids. also small kids bikes without training wheels.
I believe the bikes at Boardwalk are called a Surry. Not sure of the correct spelling.
CC also has a glass bottom boat ride that kids seem to like andit is a good size boat for your wife not to worry. They do ahve live vests for all ages aboard.
Grand caymen has a turtle farm young kids like. There is no excursion that only goes there. They have one that goes a few places including the turtle farm, but it is easy to get a taxi at the port to take you there and one back again. Not sure of the price. But if you do this, go in the morning because the traffic on the road back gets horrible in the afternoon and you dont want to run late and miss the ship!!
Cozumel is a touch one for kids, accept for a beach. I was just there in July.
I will ask my friends who have young kids and have been there if they did something besides a beach day. If they tell me anything different than a beach day I will post and let you know.
mom x4,grandma x4