In grades 1st to 3rd, I recommend saying the Hail Mary to open faith formation class and the saying the Our Father to end class. A poster of the Hail Mary helps children who have not memorized the prayer yet. (See this post for posters of the Our Father).
These 3 different Hail Mary poster sizes should meet your classroom needs. The letter-sized one can be mounted on the inside of a file folder for easy storage.
Print a size that works for your needs.
Teach the Hail Mary with Hand Motions:
Repetition helps students learn the Hail Mary faster. For add a fun dynamic nature to saying the prayer as a class multiple times, teach your students to pray it with hand motions. Loyola Press has outlined some simple hand actions that are quick to learn.