We have really enjoyed the YWAM published Missionary biographies in their children's book series. There are a few different "sets" of books. There is a "younger reader" set called the Heroes for Young Readers that are very easy to read (in rhyme) but are pretty substantial books in length and substance. I would say 2nd grade + reading level to read alone… but they are very well illustrated and very easy to listen to and are perfect "read-alouds" for little ones. Sometimes, children's Christian books can be really short and shallow, but this series really does a great job in painting these amazing people in easy to understand but very deep ways.
They also publish and "older readers" set called Christian Heroes: Then & Now and would be more appropriate for 3rd grade + reading level to read alone… but they are great "read-alouds" for any age. Reese (4) will sit and listen to these as well.
In addition to missionary biographies, they also publish History biographies as well! We've loved using these in our history studies as well!
We have been so burdened to broaden our children's (and our own!) view of the gospel and its impact on the world. We are deepening relationships with our own neighbors and are excited for gospel progress here, but also praying globally for the Lord's workers to faithfully carry out His commands to preach the gospel to the lost. With all the craziness of the worlds news (which I cannot watch/read at all), it is helpful to look back to history and study people who went through similar world trials and see their unwavering faith and commitment to Christ.
Hope you enjoy these. They would be great Christmas gifts for your own kids, grand kids, nieces, nephews, or just to add to your own library for when you have kids over!