Have I mentioned before about never learning lessons?
The internet is right, peat moss makes good digging material for gerbils.
And putting them in the empty tub to play is a great idea. Good for getting them used to their owners, and so on. Olivia was delighted when they ran up her arm and down the other side. She came down to tell me. And stayed down. And I left the not quite two year old alone with them, and he climbed in the bath... and stood on the (at that point) undamaged one. Squish.
So, it's now at the vet's, bloody, swelling and clinging to the oxygen mask. Its fate will be clearer in the morning.