The problem with measuring kids is that they are still growing. An 18 year old male is not necessarily done growing. An 18 year old girl more likely so. With younger kids it is clearly a crapshoot. I had leakages with my ileostomy and I kind of think it was because my skin didn't take very well to it. I had all kinds of trouble getting a seal. My ileostomy was temporary and I was told repeatedly by the nurses it is a whole different ball game with the permanent ileostomy instead of the loop. I don't know and hope I never have to find out.