OK, I see my sarcasm/exaggeration didn't come through right. Twelve was an extreme number to make a point. Adding ONE kid to the equation (like zuren just did) makes a huge difference on the space and priorities.
Poptops are expensive real estate--there are much cheaper ways to solve a bed in a van issue, unless you have specific requirements neighborhood covenants against parking RV's or garage heights that only can be solved with the poptop.
A hightop is a little cheaper (surprisingly little unless you can DIY) and has different tradeoffs in use.
Schoolies are cheap $$/square foot, but they are industrial park real estate--you can't park them in many RV parks or neighborhoods. They are much better for this crowd than an RV due to the strength of construction (almost on par with an ambulance). They will not shake themselves apart on dirt roads (but they will if you try to speed down the interstate).
A van-based bus is a pretty good compromise--you can get 4wd simply, more space, and still stay small enough to travel fire roads. You can add a real toilet and shower to keep the missus happy if you need to--this becomes more critical as you try to travel with a toddler. Being able to let them go to the bathroom without stopping (or only pulling over on a ramp) will save HOURS off your drive time.
You have a lot of work in your van, it is a solid platform you know. That has value. But adding on can be more expensive than trading up (just like houses).