The pair stood in two rows at the side of Westminster Hall as the new King and other senior royals bowed and curtseyed to the coffin.
The rows included Princesses Eugenie and Beatrice and their husbands, Zara and Mike Tindall, Lord Freddie Windsor and Princess Michael of Kent.
Lady Louise watched on as her parents bowed to the Queen’s coffin before, in a poignant moment, the young royal led her brother, 14, to pay their own respects in a rare moment away from their parents.
The Queen will lie in state at Westminster Hall until her state funeral on Monday expected to take place at Westminster Abbey at 11am.
Heads of state from around the world will gather for the event along with her close family and members of royal families from across Europe, many of whom were blood relatives of the Queen.
Following the funeral, Her Majesty will be taken to Windsor for a final family ceremony at a chapel in Windsor Castle.