Can’t help you with the kiddy bit but we’ve hired a couple of vans in Aus. Most of the small vans are two seater only and quite a lot of the four seater ones have the second row of seats right at the back which isn’t very social. Sounds like you want three seats in the front so make sure you specify that. Book as much in advance as you can for a good deal, don’t just wander in when you get there.
We only hired two berths so can’t really help too much but I’ll pass on what I know. Wicked Campers, aimed squarely at the backpacker market, pretty relaxed company to deal with, not fussed about the odd dink and scratch, but have pretty tired looking vans to match. Hippie Campers, part of Apollo Campers, much better quality vans but a complete bunch of charlatans to deal with. They do everything they can to extract cash out of you and took a couple of unauthorised payments from us.
Depends where you are going but the freedom you get from having a van is way better than any other option. Where are you heading (just being nosey/planning to get jealous)