schoolkids even get picked up by their teachers in big cargo bikes here in NL. i also see plenty of occasions where a mom on a regular bike will just drop the kid on a cargo rack on the front of a bike and tell them to hold on lol. with an experienced rider it's really not a big deal.
@LisaJane706 i think like most everyone else is saying a mid drive conversion would probably do you best.
i recently converted a dutch tweelingfiets (twin bike) which is what a lot of mothers here use to get their kids around. it cost me around €1900 all in which was about the same as what i was looking at for a new RAD bike. i am similar to you in that i needed a cargo bike to haul passengers around but i hated the riding experience of the front load bakfiets.
i used to have a hub drive bike, but after using this mid drive i would never go back. when carrying any kind of cargo your gears become so incredibly important, and it just doesn't make sense to have the power from the motor completely bypass your gears. the "easy" upgrade for the rad wagon would be a higher amperage controller, but i suspect even that will not be enough for you with those hills. my suggestion would be to sell it and look for a mid drive. custom builders are becoming more popular so i'm sure you could find someone to build it for you if you don't want to take on that task, or if you have more of a budget the yuba someone else here mentioned would be a great choice. i do not have as much money to blow on bikes as some of these other forum members seem to have so building was my only choice.