The tent we have can be pitched in 30 minutes. We have used it for long weekends (3 nights), less than that would be too much faff for us.
two other tips. try a childay in a pre pitched tent first....this way you can see if you love it or hate it without the expense and hassle of getting the stuff. There are lots of places in the UK and even more on the continent that do this sort of thing.
Once you have given it a go, have a look at tents that are put up! It is much more helpful looking at the usable space for real. Yeomans do this sort of thing in the East Midlands.
Once the tent is up you can see if the distribution of space suits your family needs, and if they are tall enough for your comfort.
If you decide that camping is for you, buy a recognised make of tent. there are loads of them on the market, ask on here or UKcampsite and you will get lots of advice and pointers. only buy a tent from e-bay if it is one of these recognised brand names. A lot of crap gets sold on e-bay, many of them are not waterproof enough for norther european use. American brands can be bad in this respect.
For us it was a great choice. the kids love camping, it is always an adventure for them, and they get a lot of freedom, while I get to sit, sip wine and read my book!