No. First, there are no tax credits for disabled children. As a dependent child, the only tax benefit of being disabled is that you can claim the child care credit past age 13, if the child is unable to care for themself.
More importantly, disabled for tax purposes means unable to perform gainful work (employment for money). Because of the focus on gainful work, many people with medical conditions are not actually considered disabled for tax purposes. I would generally expect that a person with diabetes will be able to perform work for money, except maybe in very rare and severe cases. You would need a doctor to certify that because of the child's condition, they are permanently unable to work.
