L.P.
Hi L.,
This is what I found on-line:
Do not put small children in the front seat of vehicle that has an air bag. Put a child that does not use a safety seat and who is less than five ft. in height in the back seat.
So going by this the child should be over 5 feet tall.
I also found this:
One of the study limitations is the lack of information in crash data systems about a child's height or weight. The study used age of child instead of height or weight because only age is recorded in the federal government's Fatality Analysis Reporting System (FARS).
L.