Turning 10 is a milestone that is often celebrated with a grand birthday party. Introduce the idea of the party with a catchy invitation. When deciding on the invitation's wording, incorporate the number 10, the fact that the birthday marks the guest of honor's entry into the double-digits age category, or the theme of the party.
Use the number 10 in the invitation and, if possible, use a rhyming word. For example, it could read something like, "It's that time a year again, but this time Sam is turning the big TEN!" or "Amen! Sam is turning TEN." Other words that rhyme with 10, that you may be able to use are: hen, pen, then and men.
Use the concept that 10 is a double-digit number, which is usually a very big deal to children. The invitation could read something like, "Come celebrate with Sam as he joins the double-digit club" or "Party with Sam as he leaps from one digit to two digits."
If you're planning a themed party, incorporate that theme into the invitation. For example, for a space party, the invitation could read, "Ready for an out-of-this-world experience?" For a roller skating party, it could read, "Let's help Sam roll into another year."