The problem with drones is that they can be very hard to control. Even the breeze from an air conditioner can send a lightweight indoor 'copter spinning out of control. Spy Cam Aqua, a submersible drone best suited for a tub or aquarium is easier because it is designed to be in a confined area and moves slower than its flying cousins.
This little sub is powered by two AA batteries. Then you need batteries for the remote control.
The remote lets you command the ship left, right, up, and down. There are also buttons that let you take (very low-rez) underwater photos and videos. And, because it is dark underwater there are also two forward facing lights.
Here is a short video of the sub in my bathtub!
The second image in the gallery above is an unretouched image taken from the sub.
The sub also comes with an arm that can hold fish food if you want to use it in the aquarium. I didn't test this feature. Frankly, I'd be concerned for the safety of the fish.
However, for water play with action figures in the tub, this toy was a lot of fun. You won't be submitting your underwater pics to National Geographic, but that it can take anything is pretty remarkable.
Though explicitly not for use in sandy environments, I would suggest that you limit its use to the tub or aquarium. Caution, and perhaps parental supervision, should be in place when connecting the sub to a computer's USB port. In theory there shouldn't be any water inside the sub where the port is located, but it certainly wouldn't be too hard to imagine some sneaking in there, dripping from the outside of the body. Water and computer parts don't mix well, so be careful.