Hi, all. I'm hoping I can get some advice here.

I've had adult American toads before, but I found a whole bunch of tadpoles this year in the abandoned swimming pool at the farm where I work. Long story short, I brought home a small group of them to try and raise. There were 11 in total, and they were doing really well, eating and swimming and generally acting like healthy tadpoles. I was/am keeping them in a good sized reptile water dish, inside a live-planted 10 gallon aquarium. There's a large rock to climb on, and some gravel that slopes upward so they can climb up as they morph. The substrate is a mix of organic potting soil and coconut fiber.

The first of them to get all four legs crawled out of the water three nights ago. He still had a pretty decent tail at that point but there was no stopping him leaving. I kept an eye on him for a few hours, and apart from getting some substrate stuck to him, he seemed to be doing fine getting around. I went to bed, and that's the last I saw of him. It's like he completely disappeared. Is this normal? Is it likely he's just hiding somewhere out of sight, or buried himself somewhere while his tail disappears? Or should I assume he somehow died?

He was so tiny, small enough to fit on the tip of my pinky finger, but there's nothing in the tank that I would consider dangerous. No ants or spiders or anything like that, the plants are all just local weeds like grass and clover taken from the farm (no pesticides). The water dish is accessible and I mist the tank every day to keep the humidity up. There are some fruit flies small enough for him to eat in there. But there's been no trace of him at all in three full days. There's another one now with all four legs, and if something happened to this first one, I'd like to avoid it happening to the second. I had thought leaving them alone and letting nature take its course would be best since I plan to release them when they're big enough, but I don't want to lose all of them this way. Any advice would be greatly appreciated!