I don't know. We all hear stories about frogs appearing to disappear. But then, of course, we find frogs that presumably create the froglets. No, I don't know where they hang out. I gather that you have one metal tank that extends above ground. Otherwise, you would simply leave it alone and dump the froglets on the ground beside the edge of the remaining pond. I assume a plausable approach would be to lay a board up to the raised edge as a bridge to where a pond plant resides.

Thanks chas. Those little guys are so cute, I don't want to lose them.

I'm having the same dilemma with a single green frog that has been residing in my plastic kiddie pool goldfish pond for most of the summer, and I've tentatively decided to capture him and move him to the bank of a brook nearby. (Our own brook, where he probably came from, is dry from the drought.) Like your stock tanks, my pool would freeze solid and crack, so I, also, will be bringing in both pool (and, in my case, goldfish) for the winter soon.

More to the point of your question, my frog is a green frog, a species that typically hibernates under water, sometimes partially buried under the mud. To hibernate, aquatic species of frogs need water that won't freeze to the bottom. Not all species of frogs do this however. Non-aquatic frogs like wood frogs and spring peeper frogs hibernate under leaves and other debris on land. So how and where your little froglets need to spend the winter depends on their species. I'm guessing that yours are also an aquatic species, seeing as they were sitting on your lily pads in the tank. However all species of frogs, whether they live mostly on land or in the water, all breed in water and begin life as tadpoles. This article was helpful to me in solving the same dilemma you are having with my own little froglet. https://www.scientificamerican.com/article/how-do-frogs-survive-wint/

Perhaps you could post photos of your froglets, so that we could attempt to identify what kind of frogs they are?

How many little frogs are living in your pool? I suspect that if you were to decide to pack them up and move them to a lake or pond near you, it would be a challenge to capture them all. At least I have only one froglet to worry about!

I hope when spring comes that all your froglets will emerge unscathed. It sounds like wintering over in your underground stock tank pond is a good option for your green frogs, and the tree frogs in the leaves surrounding it.

My dilemma ended yesterday when I moved my goldfish into the basement and drained their outdoor kiddie pool. There was my own froglet at the bottom of the pool in a state of semi hibernation. I had thought he had moved on since I hadn't seen him recently. Because his pool was being dismantled and our brook is still dry, I had no other option but to move him to the larger brook a quarter mile down the road. I think he'll do ok there. Here he was in the transport bucket on the way to the big brook down the road.

I think they hibernate by digging into some soft ground or mud somewhere and wait out the winter.

Tadpoles need your help because you're removing the water source but I think the froglets would be fine, doing what frogs and froglets do for winter.