They will meet staff and volunteers of the organisation when their 1960's routemaster bus tour of London stops at the royal residence.
The new parents will also join the royal family to pay their respects to fallen military servicemen and women on Remembrance Sunday for the annual ceremony held at the Cenotaph this weekend.
Royal fans will remember that Kate was visibly moved by last year's ceremony. The moving service honours all those who lost their lives in current and past conflicts, including the First and Second World Wars.
Kate watched down from a balcony as her husband, known as Flight Lieutenant Wales in the military, laid a wreath at the Cenotaph in London's Whitehall.