Here are a few warnings that I've seen that keep me laughing (OK, occasionally crying I am laughing so hard) ...
DEAR LORD, someone call Hazmat.
Warning: Part Monkey.
Warning: Objects in fists may be closer than they appear.
Warning: Mouth exceeds recommended noise levels. Hearing protection advised.
Warning: Laughter follows.
Warning: Will have more energy than you can ever dream of.
Warning: Remote Control will disappear in seconds.
Warning: May Contain Small Monster
Warning: You are advised to keep all hair, loose clothing, jewelry, etc. away from baby at all times.
Approach at your own risk. Parents are not responsible for any pain, injuries, or damages that will occur.