There's the Spy Kids and then there's the SPY Kids, aka the 11 millennials that unwittingly control the fate of the world's largest and most traded ETF.The $250 billion SPDR S&P 500 ETF Trust is pinned to their longevity, thanks to a quirk in the archane legal structure used by some early ETFs. Like other unit investment trusts, SPY has a set termination date and will expire in 2118, or 20 years after the last of these twenty-somethings die.On this episode of Trillions, Joel, Eric and Bloomberg News reporter Rachel Evans track down three of the SPY kids to discuss their connection to the birth of ETFs, their newfound fame -- and why they wish there was some money in it for them. See omnystudio.com/listener for privacy information.