Wow, I'm so sorry to hear this news!
From growing up with brittle bones; I can say your frog is probably in some pain you may want to get him to a vet tomorrow... See if they can do anything. I doubt they could splint it or cast it, considering its an amphibian, but maybe at least some sort of pain relief?

I honestly don't know what to tell ya here
Beat of luck though, I hope he heals soon!