What treatment is your son receiving for his diabetes?
On diagnosis it is not unusual for blood sugar levels to be gradually brought down because suddenly going from high to normal will be rather an unpleasant feeling for the patient with false hypos.
Newly diagnosed you should be in close contact with your dsn for advice on blood sugar levels and insulin doses.
The book "think like a pancreas" is a good guide to what you need to know to manage type 1.
Diabetes shouldn't impact on epilepsy management, although high blood sugars is thought to possibly increase the likelihood of seizures and low blood sugar can cause a non epileptic seizure so it might be wise to check blood sugar if there is a fit.
Depending on what medication he is on for epilepsy that may impact on diabetic management, might be worth seeking guidance from you neurologist on this.