That is odd that a beaver would be rabid.
Not that they can't, but it isn't that common.
I have a beaver skull in my office (long story) and the teeth are 4" long.
Their teeth are like a guillotine. They are all over here and at times, we have to remove them to prevent them from flooding fields because of their dams.
The child is lucky it didn't take fingers off.
I have seen beaver bite through a 2" limb in one bite.