Welcome to the forums.
Are you asking why young children acquire T1 diabetes?
No one really knows, though some people think there can be a genetic components and/or it can be an autoimmune disease triggered by a virus or trauma. It occurs more often in children with a family history, but it can still happen in children with no family history at all. And there really doesn't seem to be anything that anyone can do to prevent this condition from happening, so it's pointless for parents, friends or relatives to try to take any blame for the fact that a young child becomes T1.
Did you want to post in the Benefits forum, there is one for Children and Parents if that is more useful...? There are a number of posters there who have young children with T1.