Perhaps you could "task" them with seeing if the readings/gospel/sermon tie in somehow with your rotation topic. Since they're little, this would have to be quite simple. Perhaps they could write or draw have they learned in church that day, and then talk about it when they're in Sunday School the next week.
Perhaps, as a group, they could be given a small way to be included in the worship service -- carry the communion bread up to the altar, lead a prayer, etc. Whatever works for your church.
I have a similar issue with my 1st & 2nd grade class -- let me know if this works for you! Hope it does -- it's a great idea!