Steve,
I'll echo the other member's comments. A new or recent used mini-van or SUV would be safer with it's air bags, ABS, traction control, crumple zones, door crash barriers, etc. (Note: the newer Checkers did have side crash barriers in the doors.) The fuel mileage would be better too. The one down side to the new stuff is the high cost of repair when the electronics start to go. Between the all digital dashes, a half dozen computers, and finicky wiring harness, they can get expensive to repair real fast. I'm fighting that now in the daughter-in-law's mini-van.
If you want a collector car that can sub for a minivan on occasion, a Checker is a good option. The biggest safety issues with them are the anemic seat belts, no air bags, and no crumple zones. Plus regardless of how good an example you find, there is always the possibility of rust weakening things like the A pillars and they could crumple in a crash. I know one couple that happened to. Having been T-boned in a parking lot by a Lincoln, I can say from personal experience they do held up fairly well but there was a bit of intrusion in the A pillar area ... we did fare better than we would have if we were driving the wife's VW Rabbit convertible.
The other issue with collector cars is they can be a bit less reliable than new stuff. Over the course of 12 years and around 120,000 miles, I've been towed home twice and worried about making it home three or four other times ... and I'm a fair mechanic who can fix most stuff on the road. The two times it was towed were when an ignition module went out of the GM HEI distributor (could happen to a new car) and when I had a engine compartment / dash fire from a failed starter / fusible link. If you go ahead with the Checker, be sure to always carry a fire extinguished under the front seat where you can easily reach it; I have a Velco strip down the side of mine and stuck under the seat to the passenger side seat brace. It got used the day of the dash fire; I calmly put the fire out while the wife was freaking out. Note: the fusible link issue affects any GM car or any car like Checker that used the GM engine wiring design ...
Having said all that, the Checker is our usual choice when we take the grand-kids out ... partly because of the room and the fact it's our only 4 door, and partly because the grand-kids love riding it it!
That's my two cents worth ...
John W