Remember that though your child may get some genes that trigger diabetes - it is not really diabetes itself that is passed on to your unborn child. These genes carry some tendencies like being overweight - that could be passed on.
Studies show that in case a father has type 1 diabetes, then the child has a 1 in 20 chance to develop the same. On the contrary, if a mother has Type 1 diabetes, chances of the child getting the same are less than 1 in 50. However, Type 2 diabetes is more common and tends to run in some families as default genes - that cause it in the first place are passed on along with poor eating and lifestyle habits. So exercising caution would be a safety belt for your child.
If you are planning on starting a family, then the best thing that you can do, for the sake of your child, would be to eat healthy and also stick to a more active lifestyle. It is not really possible overnight but what you can do here is indulge in regular exercising, avoid overeating, stay more active and also have your medications on time.
If you are really worried about your child getting the disease, there are some genetic tests available for the same. These are usually done on birth - and some before birth too. This will check if the child contains genes that make him or her more prone to the same.
Along with this, there are special programs available to check and control diabetes infants. These cutting edge research programs are still in its preliminary stages. However, some parents - especially when both have diabetes history, are considering the same. But on the whole, you should consult with your doctor once before you plan for a child.