Hi Cheryl,
I've done a variation of the Rotation Model during a Wednesday evening fellowship program similar in size to yours. We put games and food before our workshops, and closed with group worship (songs, prayer, announcements). When I first got there, they were doing food first, but it wasn't enough of an attraction to get the kids to "encourage" their parents to get to church on time. Games helped and they were easier to integrate the stragglers into. Our "post-workshop" worship time wasn't fully keyed to the Rotation story, and in fact, it was kind of nice to shift gears and not treat it like "Lesson Part Two."
I've known a few Rotation programs that did an "all group intro" before breaking into workshops on Sunday morning, but was never a fan of that approach. The feedback was that "all group" gathering intros devolved into "sit and watch," and invariably took time away from the teachers and their activities.
Hope this helps.
Neil