She was chairman (1942–1948) and president (1948–1951) of the Nursery School Association of Great Britain, founder president of the World Organisation for Early Childhood Education, a member of the Central Advisory Council for Education (1945–1949), and chairman of the Advisory Council on Children's Entertainment Films (1944–1950).

During the Second World War, Lady Allen, with the support of the Home Secretary, Herbert Morrison, with whom she was friends, established a scheme whereby waste material from the bomb sites were turned into children's toys.

[2] After World War II she served as a liaison officer with UNICEF in Europe and the Middle East.

[3] She campaigned for facilities for children growing up in the new high-rise developments in Britain's cities and wrote a series of illustrated books on the subject of playgrounds, and at least one book on adventure playgrounds, spaces for free creativity by children, which helped the idea spread worldwide.

[4] In May 2024, a blue plaque was unveiled in Marjory Allen's honour, on the site of her home between 1958 and 1966 at 22 Lawrence Street, Chelsea, London.