Prince William and Kate Middleton will be waving their youngest son Prince Louis off for his first day at school in September as he joins older siblings Prince George, eight, and Princess Charlotte, six, in the milestone. The young prince turns four today, 23 April, and he is said to be making the move to a new school in September to join his siblings, according to The Daily Mail.The publication reports that William, 39, and Kate, 40, are looking to move their family to Berkshire this year and are looking at options for all three of their children to attend the same co-educational establishment. OK! has contacted representatives for William and Kate for comment.