Here are some of our favorite wording for a surprise birthday invitation ideas:

• “Shh… It’s a secret! Join us in surprising [Name] for their [Age] birthday. Keep your lips sealed and your party hats ready!”
• “Surprise! Help us celebrate [Name]’s special day by keeping it hush-hush. Your presence is requested for a surprise birthday bash!”
• “Don’t spill the beans! We’re throwing a surprise party for [Name], and we need your help to make it unforgettable.”