First of all, Jace shouldn't even be in the front seat.
Second, as a parent, I can tell you that when your child is old enough to sit in the front with you, it's an uncontrollable natural reaction to throw your arm out and try to shield your child and hold them back if you ever have to slam on your breaks. I still do it to my 215 pound 15 year old. Jenelle didn't do that to Jace. She wasn't concerned about him one bit in that instance. That's not a normal reaction.