The free play levels are intended to be optional. We added them for teachers who requested an open level at the end with a scoped tool box. They're also a place for kids who have completed the lesson to do some open ended work.
In the next version of the curriculum, we're restructuring the levels to make it a little more clear what parts are a part of the learning progression and what parts are extensions.
Hopefully people have some ideas for how to give guidance for kids who want a little more direction on these levels.