"Why was 6 afraid of 7? Because 7 ate 9! Happy 7th birthday!" "Happy 7th birthday! You're one in a melon! 🍉"
"Seven years ago, you brought endless joy into our lives. Now, it’s time to celebrate the incredible person you’ve become. Happy birthday to our superstar!"
If you're looking for a , the "7z" likely refers to the 7th birthday milestone, which is a big year for kids as they become "official" wonder-seekers.