Animation resizing problem

Hi.

So I got some cheerleading dance animations and I converted them from an adult rig to a child rig.  

When standing up straight the animation is fine and the feet are on the floor as expected however,

every time the actor even slightly bends down, sits on the floor etc, the animation clips downwards through the floor, proportionaly

to the amount the actor moves down.

I tried fixing it by painstakingly moving the Root_Bind frame by frame but gave up because these animations are 3mins long

and Blender is crawling at a snails pace when editing.  

Is there a simple way I can fix this?