My son had a pair of sports pants with an extraordinay stubborn knot in the ties. The ribbing was also worn and didn't look good, so I decided to kill two flies with one smack (aka. the Danish version of 'to kill two birds with one stone'): Instead of battling the knot, I decided to make new ribbed waist.
There is 3 cm wide elastic in the ribbing. I also made new ribbed feet cuffs.
Blogpost: Updated children's sports pants