custom interaction which has custom animation to objects

I wanna add interaction with custom animation to object

ex

object is a chair
and we only have sit or put a toddler here 
but I want to add custom interaction to the chair like pooping(...) on the chair!but EA the sims4 does not have an animation
pooping on the chair...so I am making that animation with blender.

so the keypoint is 

I wanna add custom interaction which has custom animation to objects

any one has detailed tutorial?
or knows how to do?