Sure, but so could a compact hatchback from the 80s.
The issue is this: Car seat and booster seat laws in the US have changed (I don't know what they are where I live, as I don't have kids. Sister in the US does, though). If you spaced your children 3 years apart, you could easily have 3 car or booster seats in the car, which means your back seat needs to be even larger. The VW golf from the 70s probably couldn't fit 3 booster/car seats, and might struggle with the two youngest using them while the oldest just gets smashed in the middle. Hopefully they aren't large for their age.
The issue is this: Car seat and booster seat laws in the US have changed (I don't know what they are where I live, as I don't have kids. Sister in the US does, though). If you spaced your children 3 years apart, you could easily have 3 car or booster seats in the car, which means your back seat needs to be even larger. The VW golf from the 70s probably couldn't fit 3 booster/car seats, and might struggle with the two youngest using them while the oldest just gets smashed in the middle. Hopefully they aren't large for their age.