Afrojack and Martin Garrix -- All About That Bar Mitzvah Circuit! If You're an Ultra Music Festival Honcho

It's good to be king of one of the biggest EDM festivals in the world ... 'cause it means you can score talent like Martin Garrix and Afrojack -- just to headline your kids' Bar/Bat Mitzvah!

Adam Russakoff, executive producer of Ultra Music Festival, dropped more than $250,000 for the Saturday night party at LIV at Fontainebleau in Miami. We're told his twin 13-year-olds -- a boy and a girl -- got some serious rave favors ... like cotton candy glow sticks!

The $250k tab, by the way, was just for the club and food. No word on if Garrix and Afrojack charged Adam, but considering he runs Ultra ... we're guessing this one was gratis.

Again ... good to be the king.