How “Gluten free” does a Gluten free diet have to be?

Internationally, the Codex standard for a low gluten free diet is less than 20 parts per million (ppm)  of gluten as a safe level for children with coeliac disease. This is a very small amount! less than crumbs! For children, it is also recommended that oats be avoided, because of the risk of cross contamination that can occur. Flour mills that process oats often process wheat flour as well.