Surprise your students with an uninvited guest.
Have a friend of yours who is a stranger to your students barge into your room during a lesson, start to sing loudly (or recite a poem or strum a guitar), rustle through the things on your desk, take a few items, pat you on the head and race out.

When the class quiets down, initiate a "what-happened here?" discussion centered on the intruder's looks, clothes, actions, attitude, demeanor and so on.

Distribute two pieces of paper to each of the children.
Have them label one Fact, the other, Opinion.

Review the statements and conjectures made during the discussion and help the group to decide into which of the two categories they belong.

After the lists are reasonably complete, have half the class write factual reports of the incident and the other half, opinion papers.

Ask the kids to read their work aloud.
Although some students will suspect collusion, don't admit to it.
Think of the lively conversations at dinner that night!