Re: Cure for bad knees??
Seiza will ultimately get to your knees unless its properly conditioned first. Get a full grown adult who's never seiza'd once in his life to immediately do shikko and stuff is a sure path towards that end.
So flexibility and tendon strength training is a good idea for the adult joining in.
Another thing is to reduce weight and have more overall leg muscles and good posture or body alignment. The difference of 8 pounds is huge when it comes to the knees. Imagine losing 30 pounds. Trust me I know.