From what I have been reading, the 2012 ram comes with a Standard Occupant sensing airbag. so in the seat it senses if there is a passenger and turns on the passenger air bag, if no one is in the seat, the airbag will not deploy upon a collision. I would still contact customer service and confirm this, the life of a child is nothing to play with.
Standard Features Ram 1500
PASSENGER AIRBAG DEACTIVATION - OCCUPANT SENSING DEACTIVATION
They also say the following at the RAM website "Children 12 and under should always be in a back seat correctly using an infant or child restraint system, or the seat belt properly positioned, dependent on the child's age and weight."
If in doubt, call Ram to confirm, 1-866-RAMINFO.