What can you remember?

The three girls (ages 9 1/2, 8 1/2 and 6 1/2) have been memorizing Psalm 139. They add two more verses to their memory each week and have gotten through verse 10 this week. Our goal is to memorize at least the first 16 verses. I think Daniel (4 1/2) would be capable of this as well but I haven't pushed him to do it. I think I am going to though. I really want to have them remember these verses for more then the week they work on them. I know someone who has her son repeat back old verses throughout the week instead of just the one he is working on.