R129 back seat

[Vronsky]

Fella's,
I've been deeply in love with the R129 model since ages. Lately, it seems that the prices of this model are getting within my reach so I'm thinking of getting one to drive during the Summer (and keep my W210 for the Winter). HOWEVER, I'm part of a three-person family these days, and the R129 has only two front seats. Can anyone please tell me if that space behind the front seats is suitable for carrying a 6-year-old every now and then, without causing a rebellion? I know it has some sort of cushioning/upholstery, but it's not a proper seat I believe, and mainly a place to put luggage etc.

THANKS!