Can I parent/Copy a bone from one armature to another?

I have two armatures (one for a Big monster, the other for a little-monster) and I’d like the Big monster to carry the little. Ideally, this would look like parenting (?) the root of the little monster to one of the hand bones of the big monster. But copy location in the constraints menu is not working.

Is there a simple way to do this? I imagine it’d be the same if you had a 3d armature picking up an object.