We always bathed toddlers in the washing-up sinks...bit unhygienic though I suppose!
Hilary, some caravan dealers also have tents on display - there used to be a great one at Lostock Hall near Preston but I can't find any trace of it now - however Barrons caravans might have tents too, their homepage says they do but the mainpage doesn't have a link, so I don't know...anyway
Barrons North West
Chapel Lane
Coppull
CHORLEY
Lancashire PR7 4NE
Tel: 01257 793377
and if they're no good they might be able to tell you where else to go.
We have a 6-berth frame tent - it has a lot of poles, DH colour-coded them with insulating tape, putting it up is OK as long as it's not windy and it is massive, about 16 feet long, and head room is 6' plus. (Google for Cabanon for huge frame tents.)
We go camping mob-handed one weekend a year, with various other families, and have had 7 or 8 people sitting round the table in the evening, plus lots of space around. It's great on chilly/windy/wet evenings though the windows do get a lot of condensation!
We also have a tall dome tent which is very fiddly to put up - bendy poles have to be threaded through fabric tubes - good once up though. (We USED to have a very large ridge tent but DH managed to lose it - not the poles, just the tent - it was a doddle to put up but you couldn't stand up in it. Dome tent has replaced that.)