Child Restraint conversion.

My 2 girls love riding in the wagon. They are 6 and 8, my wife would like me to have shoulder belts in the back seat but it is not a deal breaker.
The girls have named the Station-Wagon, Stan-Willy. I take them to school just about every morning. The other parents have more of a problem with my car, except for the dad who drives a restored 62 Imperial (also lap belts only).