Your child seems to be having primary incontinence (meaning: he never attained continence for a period of more than 6 months at any point in his life). The causes of primary incontinence (occurring both during the day an night) include mostly organic causes (structural causes). There are certain questions that you need to answer:
Does he continuously dribble urine?
Does he not feel bladder sensations and fails to realise that his bladder is full? In that case, the child would pass urine once in 3-4 hours, with large volume urine passage.
Does he sense that his bladder is full but passes urine while running to the loo?
Does he realise that his bladder is full, but passes urine at socially inappropriate occasions?
Answering these questions would help me guide you better.
Saptharishi L G