Working with her husband Frank, she wrote multiple acclaimed books and built a massive collection of toys that is now part of a significant museum.

Born on 6 June 1913, Caplan collaborated with her husband in authoring multiple books that studied the ways in which children played, whether alone or individually, and at different ages;[1] for example, one of their books, The First Twelve Months of Life, concentrated on infants but included observations of children two years old and comparisons with adult trade unions.

[2] During World War II, while living in northern Manhattan, New York City, the Caplans founded a workshop on 95th Street to manufacture and sell wooden toys for children.

From its earliest years, Theresa was involved with her husband's company: when it was a single small store, she worked with customers while Frank completed their orders.

[4]: 19  Written on twenty thousand index cards, her records filled twenty-eight shoe boxes by the time that the collection was donated to Indianapolis.