I'm thinking that you should take him to his pediatrician and have his blood tested, especially with a family history of diabetes. Another typical symptom that goes along with the increased thirst is frequent urination. If you have noticed this also, make sure you mention this to the doctor along with the irritability you mentioned in your posting. If it is diabetes, the sooner he gets treatment, the better it will be for him both physicially and emotionally (for everyone involved!). No matter what the outcome of the blood test is, getting him checked out will give you peace of mind, so I urge you to do this as soon as possible. Good luck to you and please post again if you need us!
Dear mcam,
My son was diagnosed with type 1 at eight years old and his first symptom was excessive thirst. He also had a family history of type 1. Have you seen other symptoms, such as weightloss, being lethargic or even bedwetting? As a mom and not a doctor, from my own experience, if you have seen other possible symptoms I might recommend taking him to the e.r. to have a simple blood test. As gg suggested, better sooner than later and with the long weekend if you recognise other symptoms, it is better to get a proper diagnosis as soon as possible.
Best wishes,
dm