T4 pop top and two kids, 6 and 2.
We got ours from a fellow STWer when elder child was 1. We "live" in the camper van in France for 1 month of the year, every year. The kids love it. We also use it as a day-today vehicle too and for long day trips to see in-laws etc it's great as there's space to go in back and deal with jr, feed, play with them. etc.
Reasons for our success with it probably a combination of any of the following:
Packing/travelling light. Dont load the van up with stuff that doesnt fit in storage spaces, otherwise you will spend your time moving it out of the way.
Learn about Communal Aires in France (in Communes, not on the autoroutes). Basically free stop over places for campervans/motorhomes but not caravans. Some of them are wonderful, some just functional. All very handy for breaking up longer trips or just providing a one night destination if you want to visit somewhere briefly. Vicarious Books publish a great guide.
Just because you can drive anywhere and stop anywhere doesnt mean you should Travelling everyday/every other day tires kids. And is v boring for them.
Local swimming baths are good for showers.
Portable kahzis http://www.thebrowncorporation.com/
Learn recipes for cooking meals in one pan on a gas hob
Mrs S and I had our best trip together cycling across the continent for 3 months. Then Jr arrived and we were worried that big adventures would be beyond us. Getting the camper van was the best thing we ever did to enable all of us to go on adventures, continue to travel light and be flexible. For a change this year, we probably wont go to france but instead will do 2 weeks in Scotland and possibly two weeks in Ireland.
Go for it!
EDIT: As for size, Id suggest go for as small as you can live with - the ability to use town centre car parks, sneak under beach-side car park barriers, climb mountain passes through tiny medieval towns far outweighs having room to take tons of stuff with you. We use a large pop up to create a base camp (see photo up there ^) for more space when we need to.