It's almost always better to involve kids in the process. Worked in Cub Scouts, worked in Boy Scouts. Worked with the parents of Cub Scouts and Boy Scouts. And it works with me too.

Film photography is all about delayed gratification. Not a concept that develops early in life. So something tangible helps. Was easier when Polaroid film was cheap and plentiful - let the child take a few shots with the Polaroid to get in the mood. Just not the same with digital - it's not as tangible - but perhaps still helpful.

I haven't tried with large format, but I would guess the oddity of a view camera and seeing the reverse image on the GG might help pique interest and foster cooperation.

Also, I happen to believe (but no proof) that getting down on their level helps. IE sit on the floor so you aren't towering over them.

You can pretty much bet that any forced pose will not be worthwhile. But I've seen "studio" photos on the walls of friends and family that I thought were trite and formulaic. Yet they liked them. It's all in the eyes of the beholder.