Before you start selecting signs at random, think about what your ministry needs and start there. What do you hope to accomplish with the signs? Non-religious signs may help the children better understand what you want them to do, and could possibly be more helpful for classroom management. If you hope to encourage more participation in worship for those with limited speech, adding signs to songs may be a good starting place. Still another area of focus may be teaching signs based off of the main vocabulary of your lesson.