Diabetes is a genetic disease, meaning that it is passed down from parents to children through genes. In the case of type 2 diabetes, which is the most common type of diabetes, the disease is caused by a combination of genetic and environmental factors.
If both parents are heterozygous normal for diabetes, this means that they each carry one copy of the gene for diabetes and one copy of the normal gene. When these parents have children, there is a 1 in 4 chance that each child will inherit two copies of the diabetes gene and develop the disease. There is also a 1 in 4 chance that each child will inherit two copies of the normal gene and be completely free of the disease. The other two possible outcomes are that a child will inherit one copy of the diabetes gene and one copy of the normal gene (making them a carrier of the disease, but not actually developing it), or that a child will inherit one copy of the diabetes gene and one copy of a different gene that protects them from developing the disease.
It is important to note that the chance of having a diabetic baby is just that - a chance. It is not a certainty. Even if both parents are heterozygous normal for diabetes, there is still a 3 in 4 chance that their children will not develop the disease.