I went camping in our 5m soulpad with my 3 children and my friend and her 4 children (4 of the children are large-ish - heightwise) and it was fine. We had room for all our stuff and their stuff at one end as well. To sleep on - I got 10 cm self inflating mattresses for me and DP and I think they are really comfy (got them from Tescos and paid for them with clubcard points). The children also have sims but not so thick. We had to buy a roof box for the car as well, as there was just too much stuff to fit it all in comfortably - I like to take lots of duvets and pillows in pursuit of comfort. Then also needed to buy a fire pot which was really exciting. Had to get solar powered fairy lights (reasonable in B and Q). But Poundland do some good metal cups and plates for camping. It is a bit scary if I add up how much we spent, but figure it's an investment.
I have seen a great set up with a bell tent, a utility tent for cooking and storing stuff, with a canopy between them. Made the space much more useable, but probably not suitable for places with defined pitches
OK let's put it this way: freezing temperatures, many many layers of clothing just to stay alive, sleeping children and dog 2 feet away not to mention the rest of the campsite potentially listening in. Not the most romantic choice of holiday, no.
We fit 6 in a 5m bell tent no bother. We tried the 1/2 inner but found it broke the space up too much and made it feel overcrowded so we sent it back.
Beds get stacked up in the daytime, kitchen equipment lives outside (windbreaks and tarp to make a porch area).
It's a very communal sort of holiday, all crashing out on mats to sleep.
And set aside the pretty glamping idea, the amount of stuff you need to take for a family of 6 does spoil the effect somewhat and there's only so much a bit of bunting can do. We hired a big trailer for our longer camp last year and chucked anything we weren't using in there till needed.
(I wouldn't say camping is a mega-cheap option, if I add up how much we've spent on camping in the last couple of years I'd be a bit , and larger families do get hit with extra costs at every campsite, those pesky extra children!)