2000 Hyundai Elantra air bags problems

I was driving north bound on highway 99. On a saturday afternoon in rush hour, in sacramento, ca. When I was hit on the rear passenger side by a black nissan. When the cars touched we spun 3 times in the middle of traffic. We were lucky enough to not hit any other vehicle. The car stopped 8 feet away from the retaining wall, facing north bound. My infant (1 month old ) and 13 yr. Old were in the back. The infants car seat sifted about a foot towards the left of the drivers side.

In head on collision, estimated speed on impact roughly 20-25 MPH--airbag did not deploy---should it have? Not sure what speed would caue airbag to deploy- if there is a defect in my airbag system,because it did not deploy, resume with a class action, which I will check off, if there is no recourse or reason why my airbag did not deploy, I feel that it should have, but anyway, if there is reason to substanciate the air bag not going off, the I will disregard the class action. Please reply asap if possible.