Hmm...the last of the 10 toadlets I'm raising have just lost their tails, so I hope I can help. What exactly is terrarium carpet? If it's something like Astroturf, it could be abrasive or could contain some kind of irritating chemical that affects amphibians more than reptiles. Floating platforms could be difficult for the toadlets to climb onto and off of easily, so you might want to replace them with rocks that extend slightly out of the water or some plants like Java moss that provide access to surface air while allowing the toadlet's body to remain in the water. Another easy way to provide access to the shore is to tilt the container you're using and prop one side up to create a land area.
I'm not sure at what point exactly the tadpoles switch from gills to lungs, but it's probably a good idea to make sure that they can keep part of their body in the water at least until the tails have lost the transparent fin/blade part entirely and have been absorbed up to about 3-4mm. Five hours after the appearance of front legs seems a bit early for coming out of the water entirely, although I'm going by my observation of American toads.
I doubt that the your toadlets are dying of starvation, as they don't seem to need to eat while they're still absorbing their tails. However, it's not a bad idea to have some aphids, fruitflies, etc. available, although you probably know that already having raised toads before.
Hope this helps...if not, some specifics about the species you've got, the setup you have, and the appearance of the dead toadlets (i.e. dried out, bellies shrunken, bloated...) might help determine the problem. I have heard about "spindly leg syndrome" which sometimes occurs in toadlets if the didn't get the right nutrition as tadpoles.