A handful of scattered thoughts...
That's a wide age range, which is difficult for many teachers. You might be tempted to simplify things for the sake of the younger ones, but that's the wrong strategy. You MUST engage the older ones. If you lose the older students, you lose the class. But if the older students are engaged, the younger ones will follow and try to keep up. So, as an example, although I love Songs for Saplings and am glad to see them get a shout-out here, I probably would not use Dana's songs with your group because those songs are aimed at younger kids and you risk signaling to your older students that they can check out.
You have a tough topic for kids. Even the oldest ones still think more concretely than adults, so take your teaching beyond concepts and make it about real people. Use the Bible's stories. Teach about real prophets, real priests, and real kings in the Bible—and then show how they point ahead to Jesus and how Jesus is better. If I were assigned to teach prophet/priest/king to kids, I might teach through the opening half of 1 Samuel. Seriously. Because that part of the Bible shows, in concrete terms, how we need a good prophet, priest, and king. You will use the catechism too, of course, but adding some story makes things concrete, and kids need that to be engaged.
Think about how to be visual. If you aren't teaching visually, most kids will not be engaged. For every key point you tell, have a corresponding way you show that truth. This is not about being cutesy, but about having something that engages the eyes as well as the ears.
Ask thoughtful, well-prepared questions that have more than one good answer. Then listen carefully to how your students answer, and engage with their answers. Obvious-answer questions are deadly and signal that you aren't really interested in what your students are thinking. Not really stopping to listen to their answers (probably because you're thinking about the right answer you already have in mind) is also a sign you aren't interested in your students. Kids are engaged when you are truly interested in what they are thinking.
Since you have an hour, think of several ways to reinforce each lesson. Besides direct teaching times, you might have written activities, games, songs, something creative. And I think you should spend a good chunk of the time praying with your students. The prayer time doesn't have to connect directly to each lesson's topic; just take time to pray as a class. It's how we practice faith and acknowledge that Jesus is the Christ, and it's an opportunity for you to connect with your students if you also discuss what to pray about. Make this time relaxing and unpressured. Enjoy learning about their lives and finding out how your class can pray for each other and for your church, and then pray together. If some kids prefer not to pray aloud, that's okay. You can do the actual praying. Jesus' own method of children's ministry was to gather kids around him and pray for them (Matthew 19:13).