Hi, we live in one two weeks a year with 5 dc and love it. The layouts differ a lot between statics, check carefully that it works for your requirements - number of bedrooms, space for cooking, walkways/doors, lounge layout. It's small which is wonderful as you have to be compact and organised - you don't spend ages looking for things or tidying, as it's so tiny you can't take much stuff. You do need to have a laundrette nearby (and not take your delicate laundry). There is no bath but we washed babies in the washing up bowl and showered them when they got too big for that.
Location is the main factor. A static well spaced in an amazing location with a view where children can play out safely is an entirely different proposition from a static in a basic crowded park. I have heard of some statics costing £200k in desirable locations.
Well, I'm not sure I qualify as a larger family (3 DCs) BUT we do own a static caravan in Devon.
It's great but the one main thing you need to be sure of is that you have taken into account ALL of the costs involved before you start. It is a very expensive hobby! On the park we are on, caravans start at £20k for a basic 2 bed up to £100k plus for a more upmarket lodge style caravan. The cheapest with central heating & double glazing would be around £30k and would probably be second hand. Add to that the annual site fees of between £4k & £7k (depending on pitch), insurance, maintenance, rates, petrol to get there and back etc.
We have had ours for 8 years and love it but just wish someone had laid the true costs out for us before we bought!