Which sentence contains a nonrestrictive clause and is punctuated correctly?

The teacher packed picnic lunches for all the students—which they loved—and ate lunch outside with them at recess.
The teacher packed picnic lunches for all the students which they loved—and ate lunch outside with them at recess.
The teacher packed picnic lunches (for all the students) which they loved and ate lunch outside with them at recess.
The teacher packed picnic lunches for all the students which they loved and ate lunch outside with them (at recess).

The teacher packed picnic lunches for all the students, which they loved, and ate lunch outside with them at recess.