I taught them to say Hail Mary when going to bed. Our Father at a meal. Glory be however. The children love pictures. So, there are some booklets with pictures. Let them know that the pictures start with Mary and the angel and how each picture takes you through the life of Jesus, Mary, Joseph.
I took tablet paper, wide lines and wrote out the Hail Mary, and put in the plastic sleeves you use for note books, this was later about age 6, 7 for reading. They know the prayer by heart and now can say and see the words. Do the same for Our Father and Glory Be. Then the Apostles Creed is last and I printed it all out.
Our grand daughter, slow learner picked up on it real fast. It is a like a light comes on after they know the prayer by heart and then can see the words.