When teaching a memory verse, be sure to provide a take-home of the verse to help the children practice the verse and be ready to recite it from memory next week.
I like to use a page layout program to create an attractive full-page take-home - something that would even be nice enough for the children to pin up on their bedroom wall or on a bulletin board at home. This makes a nice reminder whenever they walk by and you could encourage them simply to recite the verse every time they see it. If they do, they will be sure to remember it. If you teach a clear application (or challenge,) this will also be a reminder to the child to live the verse too.