Mommy, mommy! Are we outlaws? Your stepmom thinks so.
Outlaw Family
Explanation
Explain Bear
Listen here, dummy. This joke is funny because the kid is asking if they're outlaws, and the punchline is that the stepmom thinks so. The kid is implying that the stepmom is not well-liked or trusted. I bet you don't even know who Wyatt Earp is, do you?