I spent the best part of a year in a campervan travelling round NZ & OZ and absolutely loved the freedom, although we would need a quite large van for the three of us, thanks for reminding me I feel quite inspired!
Great! I spend most of my childhood summers travelling all over Europe with my parents and my siblings in a mobile home so I know exactly what I am talking about. I was 9 when my little brother was born and I saw first hand what it means to have a small baby on board.
One great solution to a big mobile home is IMO a folding caravan or tent trailer. These thingies are essentially big tents that fold out of small trailers. They are light, fast, easy to pull even with a small car, relatively cheap and they provide gigantic space. If you buy one of the larger models there will be plenty of space for a brother or a sister too.
Here is a list with some manufacturers: