I have no idea about the title of this book. It is one I read (and owned) in my childhood. I think it was sent as part of my subscription to a children’s book club–perhaps Children’s Literary Guild. Probably I encountered it between 1940 and 1946. Plot was about a child–I think a boy–living rural, who went to a visiting circus. There he encountered animals who he could somehow make small and take home with him.