Dynamic Model Deformation?

Using Blender > Unity, I want to create two creatures, one an adult, and one a child that is basically just a simple model deformation of the original one.
Obviously that’s easy, but then I’d like to set up a progression between the two that I can manipulate to simulate an aging process. So basically it slowly shifts from the child model to the adult model.
I know I could do this with an animation, but I’m pretty sure that would preclude other animations from working alongside it; it wouldn’t be just a base state of the creature.
Does anyone know of a way that I could handle this?

…I misinterpreted what this forum subsection was for. I thought it was for using Blender models in games; didn’t even know Blender had it’s own game engine.