What are the expected uses for this RV? You mention daily driving; for many people, even a class B (van conversion) motorhome would not make the best daily driver, though certainly better than a large motorhome. How much time do you anticipate camping, and in what sort of weather (i.e. cold, cool, hot....)? Will you be camping away from hookups for more than a night or two? Will you be taking longer trips, or weekends mainly? How much privacy do you need from each other? How tall are you and your son...and how quickly is he growing?
Very generally speaking, a larger RV will probably be more suitable for longer trips and longer times without hookups as it will have more storage room for essentials and larger tanks for water, propane, and so forth. There is a lot of variation here, of course, and people do take long trips in small RVs all the time, so it's not a complete hard-and-fast rule.
A pickup camper might be another option to look into, besides a van. They all have their advantages and disadvantages.