Diabetes is grouped into two types Type 1 used to be called insulin-dependent and juvenile-onset while Type 2 was referred to as non-insulin-dependent and adult-onset. Most cases in children are classified as Type 1. It is felt to develop from the body's immune system making antibodies (things in the blood that generally help to fight infection) which then damage the cells in the pancreas which normally make insulin. This happens at different rates in different individuals, so the disease can present at various ages. Type 1 equally affects boys and girls, but is more common in Caucasians.
Without enough insulin in the body, one can see the classic signs of diabetes polyuria (peeing a lot), polydipsia (drinking a lot), and polyphagia (eating a lot). Sometimes kids can also have some weight loss. I understand totally why you are thinking that his symptoms could be associated with diabetes, but let's not label him until a diagnosis is made. With a family history of diabetes, you are more familiar with the disease than others. There are also several risk factors and immune-related markers that some specialists may be able to use to predict diabetes, particularly in first-degree relatives of patients with diabetes.
In summary, I do not think you are overreacting. It would be very appropriate to discuss this with your pediatrician and to have your son examined.