My choice, although with only two kids, was to keep our two daily drivers, minivan and older F150. We then bought a new tow vehicle. Our choice was a SRW F350 diesel, but there are tons of things that can fit your needs such as full size vans etc. A coworker has four kids and they use a mega cab ram 3500 as their tow vehicle. Don’t discount the ability of your nine year old to sit in the front, if they aren’t big enough yet they probably will be wishing the year, so maybe don’t use that as the decision. Also lots of the full size vans are really nice now!
I actually really like having a tow vehicle that I don’t use for much else. That way when it is time to go on trips it is ready to go. It can be hooked up and when I get how from work in the beater F150 we can just hop in and go. Also the tow vehicle can be used as backup for the daily driver if one of them is ever in the shop, letting us drive older daily drivers then I would be comfortable with if we didn’t have a backup.
