If you're looking for a book series that will get your children excited about serving the Lord, then I recommend The Missionary Adventures Of Bob And Arty. There are five volumes that I have found and they are great!
Bob and Arty are homeschooled boys who are trained by their father for a missionary aviation ministry. You get to travel with these young boys as they face hostile natives and jungles and mysteries of the seas. Children will see how a servant's spirit and Godly attitude can help guide through the roughest perils and the loneliest situations.
Does your child have a heart for missions? Do they desire to serve God, but aren't sure exactly how? Author Jeff Barth is hoping that these books help build a child's faith while giving them a heart for evangelism and service.