Thank you for you comment, I’m glad you were able to hear and rescue your babies. I feel like that needs to be something that pops up when you do research for a critter nation! Luckily my other girls now are getting bigger and have no desire to crawl underneath.my baby rats also would go under the tray (replacement tray) and get stuck, however no deaths. I would hear the squeaking and grab them. The rats below would attack them. Finally they grew to the size that they couldn't do that anymore.
Sorry for your loss.