I’m trying to animate a woman carrying a baby, but I have run into a problem. I’ve animated the woman, but have no clue on how to attach the baby so that it moves with her. I can accomplish this with a simple object, but not an object with its own armature.
Am I trying to do it absolutely wrong in trying to keep them two separate armatures?
The baby just needs it’s own action that matches the woman’s action. What you want to do is not easy but is doable. The hard part is switching between the woman’s action and the baby’s action while polishing the animation.
If you are not going to see the baby, for instance if it is swaddled and the face is not very visible, you could turn the baby into a prop, parent the baby prop to the woman’s armature, and then on close ups, switch your shot to use the baby’s armature.
Good luck!
This sounds like a perfect time to use a ‘child-of’ constraint. Funny really 
Depending on how she is holding the baby, you could add the constraint to the baby’s torso/hip (COG) bone, parenting it temporarily to (say) the mother’s torso, or forearm bone. Then you can freely animate both characters but the baby will be linked to the parent, err. I mean, mother. 
So just pose both characters as you want them, then add the constraint to the baby’s bone (in pose mode, if my memory is correct). After you add it, the baby rig will probably jump to a weird position. If so just press ‘Set inverse’ in the constraint panel and it should snap back to where you put it. Then animate away! No counter-animating required.
That was exactly what I was looking for, thanks.