I am not a CJA member but some things to consider:
Babies have a large heavy head relative to their bodies, weak neck muscles and need to have their heads supported to prevent spinal injuries. What age are they able to support their heads effectively in a jostling Jeep crossing rough terrain? Not sure on that, maybe age 3/4, assess your child's abilities. Not aware of any readily available (outside the medical system) neck supports, C-collars for babies/small children. I'd leave the babies at home.