There are plenty of Things to Do links. Attached is an example.
A couple of mine:
Take a morning boat from Westminster to Greenwich. Fabulous way to see London from the Thames. In Greenwich, see the Royal Observatory. The kids will learn how time was standardized.
Churchill War Room. No need for reservations. Just arrive 20 minutes before it opens.
Regents Park. A classic quintessential London park— very scenic — good spot for family Christmas Card photo
Harrods— kids will love seeing a store like that, especially the foods department.
For London’s finest ol’ school shopping street, walk down Jermyn Street.
Hamstead Heath
Little Venice in Maida Vale
Wimbledon
Kensington Palace (in Hyde Park) has some good tours that are less known to the public.
Chelsea Gardens
Link: https://www.timeout.com/london/things-to-do/101-things-to-do-in-london