Here are some comrprehensive sources with lists of interviews with children's authors, from picture books to young adult.

Kidlit Interviews Wiki - The Kidlitosphere (blogs and podcasts about Children's Literature and Literacy) is filled with interviews of children's literature creators and children's literacy promoters. This site will take you to interviews with creators of children's books and promoters of literacy from all over the kidlitosphere. Just click on a category and go!