How does Celiac's Disease cause people to stop growing?
The "proper" term to use in a case of growth retardation in children is "failure to thrive", abbreviated as FTT.

Celiac disease is one of the most common Organic endogenous (genetically based) FTT syndromes.

The main cause of FTT in pediatric celiac patients is malabsorption. In a case of insufficient vitamins and nutrients absorption the child will (have) FTT.