Yeah, that is really all you can do at this age. try to set them close to how they normally just stand. I like to set them duck with even angles because at this age, kids tend to move their entire body as a unit. They don`t have a whole lot of upper and lower body separation yet so in order to keep them aligned well with their board, you need to use a symmetrical stance. Having anything other than this can cause rotation issues when they try to control their board.
I disagree, I think you would be hard pushed to find a little girl that like to ride stacked up on her board. Most kids, especially girls, like to ride a little open, having less of an angle on the back binding helps them out. They don't have the strength to twist the board, and mostly rely on rotational movements of the body to turn. Most kids will ride with a good deal of separation, and not in the right way, but it is what it is.