Do you have a Touring or Touring L (leather seats)? If you put your van info in the signature line of the UserCP it might help us answer your questions.Anyone else get a different answer on this? Chrysler told me that the dial doesn't do anything in my model. I find it odd -- I do have an extra PWM dimmer which I may try retrofitting once the warranty is expired.
In my 2017 Touring L, the roller switch on the right controls the interior lighting and dash brightness and can completely turn on or off the interior lights if you click past the rolling part at either end.
The rolling switch on the left controls the brightness of the ambient lights (light by the door handle and a tiny rectangular light in the overhead console plus a few other lights). To more easily see the ambient lighting (if equipped), turn on the parking lights and ACC (accessory mode). To see how much variation in brightness there is you may need to sit in a dark garage or check at night.
It is possible that a Touring doesn't have ambient lighting, so the left roller switch may be useless. They just didn't want to make a plug for that space to put in place of a roller switch. The Touring came out after the initial roll out of the Pacificas and the manuals aren't always as updated as one would hope.
As far as kids playing with the overhead lights, shades, etc., once the curiosity of the van features wear off, it shouldn't be as much of a problem. If it continues to be a problem, then it is a discipline issue and they will need to learn what the rules of the van are. You could tell older children that it is distracting to have the lights on at night and for them to ask permission to turn lights on. For a smaller child you could try a different place in the van or a carseat that doesn't allow him/her to reach the light switch. Kids will learn what is acceptable behavior. Better to start working on problem behaviors now. If you really want children to have lights on in the van at night, then you may have to accept that the lights are bright.