Nico di Angelo: January 28th

Piper McLean: June 3rd

Grover Underwood: June 5th

Frank Zhang: June 5th

Jason Grace: July 1st

Leo Valdez: July 7th

Annabeth Chase: July 12th

Percy Jackson: August 18th

Hazel Levesque: December 17th

Thalia Grace: December 22nd

I'm not sure if all of these are accurate because I'm too lazy to look it up officially. I got these of Instagram. If they are wrong leave a kind comment and I'll change it.