Hi, Cheryl! Welcome back!
My suggestions are based on Sunday morning experience, but I think they will work for Wednesday nights, too:
- To give early arrivals something to do until the "official" start time, my church did "Buckets of Fun," where small groups (age groups) could grab an easy to jump into game (card game, Jenga, magnet building tiles, ....) off of the shelf and play that with their Shepherd and group until start time. You can see that idea and others here: Problem with children arriving at different times.
- We then had a large group time that lasted about 15 minutes before the students went to their workshops. We would practice the memory verse for the rotation, sing a few fun, active, worship/praise songs (bonus points for songs that tied into the Bible story), sing Happy Birthday if there were any birthdays that week, make announcements, and pray. Those who wandered in during that time did not miss any "content" and everyone could start the workshop activity together.
Another thing to notice is that many of the lesson plans at this site include early arrival activities for that same reason.