This is a simple physics question. Velocity is what causes the most damage to human occupants. You don't really have to come in contact with anything solid to suffer severe injuries.
In the case of a head on collision, your velocity goes from upwards of 65 miles per hour, to zero almost instantaneously. It doesn't matter what bumper you have, it's very hard to survive that sudden drop in velocity.
Adding a sturdy front bumper, bolted directly to the frame, does more to increase your total velocity by taking away the vehicles natural tendency to crumple and absorb energy. Even though modern cars are engineered to maximize the crumple zone and absorb more energy than ever before, classic cars still crumple and absorb energy.
ARB bumpers are designed more to protect your truck in lower speed collisions than anything else. There's a reason they are not safety tested. You're better off without them. But they sure do look cool!
As someone already said, the better money would be spent on modernizing your braking system and updating your seat belts Nick. Also, good tires and a complete inspection of your suspension and steering system to improve your cruiser's handling is the way to go.
All and all, don't worry too much, when we were growing up, we'd sleep in the back window well on road trips. We never used seat belts, and we still survived. It's like my grandpa once said to me when I told him about my fear of flying... He said "if it's your time to go, it's just your time". Enjoy the ride my friend and congratulations to you and your growing family!
PS. What if it's the pilot's time to go?