Henry is not living with his parents in the 1939 Register. As an 18 year old at the outbreak of war, he may have left the family and/or joined the Armed Forces. That said, there is no evidence that he served and with his father's experience he may not have been encouraged to. He can't be found in the 1939 Register elsewhere, but it is possible that his record would also be closed, expecially as his was a late December birth.
Other information:
A Lance Bombadier H HOOLE of a searchlight battery in the Royal Artillery (No 17772654) was wounded in Malta on 6 Mar 1942, but this was a Herbert HOOLE.