If you are an educator or librarian, sign up with libro.fm for a free account with ALC and free access to audio books for children.
If you have a Kindle reader, Amazon offers a selection of free children's e-books for Kindle.
If you have a Nook reader, B&N offers a selection of free children's e-books to use with a Nook.
Bookflix from Scholastic is an online literacy tool that pairs up fiction with nonfiction with engaging videos, read-alouds, vocabulary games and other literacy activities. During the COVID-19 school closings, a free login is being offered:
user: Learning20
pass: Clifford
Otherwise, you can create a free account for educators and librarians for full access.