Check out a Catholic bookstore. I have a pack of Saint cards that I go through with the kids as a filler. I make up games like Name that Saint or "Are You Smarter Than a Faith Formation teacher?" Instead of hangman, we draw angels with the words in their lesson book. Have them form 2 teams and take turns answering questions about the lesson. Bring a few pacjs of gum for prizes for the winning team. Or ask for examples of people they know that did something that Jesus would have done or talk about ways for them to get involved in the mass. 4th graders are anxious to share stories and experiences and are great contributors to your lesson. Have fun.
This is the first time I ever heard of putting those 3 grades together, and yet with a small group of students. There is plenty to teach and do to fill an hour.
I teach a 5th grade class, and I never have enough time to finish. We then continue the lesson, the following week.
They love to make things and learn as they do. This year we made a craft of the Miraculous Medal and learned all the symbols on it, the prayers that it contains. It took more than one class to learn the meaning of the symbols. I will put in a site from a home-school place I visit for craft ideas. The large medal is made with aluminum foil, and looks like a medal. They worked on it in one class, but we were rushing at the end to finish gluing and tying a ribbon on it for them to hang up at home. They wanted to take it home with them that day and loved it. We didn't paint it, although you can, I kinda like it unpainted, but you will need another class just to paint it.
I am still teaching the rest of the symbols and meaning. Took each one and they understand more about it and it is meaningful to them.