Everyday during our training period we have a “reverent time” where we practice being reverent. During reverent time they sit on the couch with only the activities they are able to use at church. We use a timer, with small amounts of time that increase as the days go by. While the timer is running they must sit on the couch silently and do their activities. When the timer goes off we get a reward, either a tiny treat or a fun activity.
At the beginning of this training time the timer only runs for about 2 minutes. Every day I move it up a minute until we are doing reverent time for 15 minutes a day. Its a small, short amount of time to practice sitting still reverently, but it really does start to help them sit better during church. When the kids seems to be getting a grasp on sitting reverently and they are doing better at church, then you can stop the reverent training times.
Practicing the behavior that you expect for a few minutes everyday will really help you children be better prepared for the longer stretch on Sunday.