After teaching the memory verse, give one of the children a checkered flag. (Note: I suppose any type of flag would do - although you will not want to dishonor your national flag by using it for this purpose.) Explain that the child will now, at any time during the club or class be able to stand up and wave the flag to get all the children to recite the verse. However, they should not wave the flag while another activity is going on, but try to do it between songs, Bible lesson, missions time, etc.
Obviously, you will also have to use discretion in choosing which child gets to use the flag.