Some children you teach may have a good foundation of Bible knowledge already. So a problem could be how to keep these “I already heard that before” children interested while teaching children that are not as well-versed (pun intended) in Scripture.
All the children we teach enjoy it when we teach about a not-as-well known portion of Scripture. For instance, I don’t believe we have ever heard a child say that they had already heard the lesson we have taught about God defeating the Ammonites, Moabites and Mount Seir for Hezekiah when they marched with the choir out front. (II Chronicles 20) Or when Jehoiakim cuts up the scroll on which Jeremiah had written God’s words. And how God responed in a way that showed that His Word could not be destroyed. (Jeremiah 36)
To make it more interesting, tell one of these kinds of lesser known and taught lessons without telling who the main person is. Refer to them as “a king” or “a prophet” until near the end of the lesson when you let them in on the fact that this is someone that they’ve already heard of.