Yes, unfortunately. Car seats and booster seats are hard items and they don't have joints to move bits out of the way. People are squishy and have moving parts.

Yes, unfortunately. Car seats and booster seats are hard items and they don't have joints to move bits out of the way. People are squishy and have moving parts. The adults won't be comfortable if they are thicker, but they can squish in - often, quite literally. The solution to this would realistically be to have built-in booster seats or a different style of seat belt that would better fit children and eliminate the need for booster seats for the older children.