Fire belly toadlets dying with mouths open

[lmcca996]

I realize that toadlets aren't as hearty and require lots of feeding and cleaning - which I have been very good about (cleaning, dusting flightless fruitflies with the best vitamins, broad spectrum bulbs, adequate space, water filter, heating, moss substrate, using Tetra water conditioner, etc.). I've had my toadlets since August and had to undergo some tough learning experiences involving needing to change vitamin regime and increase the size of their tank, which was possibly causing the initial die-off. Since, I have a had some luck with my babies and many of them are growing rapidly and look very healthy. A few I've had to isolate in an attempt to make sure they were eating - which I soon realized that they were not - and randomly I will find these 'starving' babies dead with their mouths wide open. Have you seen anything like this? Is there something I've done wrong that these babies choose to not eat when given more than suggested?

(Below is a picture of my babies prior to habitat/diet changes, and a picture of 'King Tut' one of my happiest adult toads!)