Those piped shirts are to George & Louis what coat dresses are to Kate.
^^this.
Total work uniform - he's seen in this for everything formal (bar those bizarre page boy outfits at weddings). From the pix with newborn Charlotte right through to on the BP balcony at Trooping the Colour,
Only question is, will Louis wear the handmedowns from George or will he get his own colour? Grey? Red?
Charlotte's look is similar, though less obvious because it's more timeless (less Blitz orphan, more cute girly frock).