Remember the old Toughskins boys jeans from Sears. They had a piece of extra fabric the width of the pant leg and long enough to cover the knee area. You could do that. Sew if into the seam. If it's felled, or sewed down, stitch along the seam. The tuck in the edges of the hole and sew it or glue it down. And tell Santa he needs knee pads.lol I do stuff like this all the time for my two.