|I just read the tip of RobinH on sewing in labels in the back of pants so the kids and DH can see wich side is the back/front.
So, this is how I do it, because we do have the same 'problem' here.
I just sew a button at the CF, keeps the elastic from turning and if neccessary, you can distribute the fabric a bit, so there is more at the back and the front is more flat. I stich in the ditch at the side seams and Cfseam as well.
I have so many single, plain or unused buttons from 2 generations back, and the button is allways the front on any pant.