If you want to try it out without investing several hundred thousand dollars, here are my thoughts:
With just 4 to travel I would look for a motorhome, either gas or diesel, that will tow a car that will seat all for and a little extra for shopping etc. We towed a chevy tracker with a 97 30' motorhome on a Ford 440 with no problems, well over 100,000 miles, living in it for up to 6 months at a time, with 2 large dogs instead of the kids. Of course the dogs often slept on the floor!
Some years ago we met a lady with three kids traveling all over the Americas with three kids about the ages of yours. The were trying to visit as many World Heritage Sites as possible in a year. They had already done the far east (not China) and after Central America were going to Ireland, renting a camper van there and doing Europe! Daddy flew in to meet up with them when work allowed--he mostly had to stay home and work to pay the bills!
After a few months or so you will probably know what you need and or want.
