This site on the whole has religious texts, religious topics, etc. So, it wouldn’t be my first choice for secular Hebrew books. But, there are some good choices here so I’ll list the pages that are relevant.
Children’s books are here: http://www.nehora.com/categories/Children/Childeren-books/
Dr Seuss in Hebrew: http://www.nehora.com/categories/Children/Dr.-Seuss—-%28Hebrew-translations%29/