Bruises heal faster in children than in adults. And I still haven't heard any serious evidence that this is the same child, like an explanation by law enforcement of how they confirmed that the child they have is same one seen in the video.
People often become dizzy and disoriented when punched in the head, which might explain the mild kicking. And kids who are beaten regularly learn to stifle natural instincts in order to avoid further beating -- this kid wasn't doing anything for at least a couple of minutes leading up to the beating; just imagine what the punishment for kicking mom would be!
As a child I wore long sleeve shirts and pants in the summer to hide the bruises and welts on my legs and arms.
And for me they took forever to go away.
Had I tried to run away or kick back I would have been beaten even harder.
This woman is dangerous. Take it from someone who knows.