My tadpoles are coming of age!!

[JimO]

It's normal for the front legs to form beneath a layer of skin, but they are supposed to pop out just before the tail starts to be absorbed. The three out of 50 is probably not an abnormal mortality based on problems with formation of the front legs. If it was me, I'd try to help the last guy free his legs if it looks like he will die otherwise. But, not to worry, if there was a serious external cause, I suspect that most of the frogs would have been deformed.