No, this passage is describing the care they needed.

It doesn't make any sense as an interpretation to jump right to death if you look at what the passage actually says. They died because they couldn't clap their hands? They died because they or their caretakers didn't smile enough (gladness of countenance)? They died because they didn't get enough gentle encouragement from their caretakers (blandishments)?

This was from a list of fucked up things Frederick II did written by a guy who hated him. If the kids had died as a result of the experiment, surely it'd say so. It's just saying the experiment was a a failure (labors were in vain) because of course they did not spontaneously start speaking Hebrew, Greek, Latin and instead had to rely on nonverbal communication.

If someone says "I can't live without my phone," they aren't going to literally drop dead one day if they forget it at home.

If you have a source laying around for info on the kids' deaths, I'd take it.