Even after the adventure is over, Stark is apparently convinced that the bad guys are completely wiped out and that no one would ever think of targeting Harley, because he invests exactly zero SHIELD resources into protecting the kid and essentially disappears from his life like an incredibly snarky imaginary friend. They might as well have filmed a post-credits sequence where the kid is tied to a table in a Hydra base getting interrogated by a snake-headed man, because that's almost certainly what happened after Tony left.
"Wait, how do I use this?"
Ever the learner of lessons, Tony continues his child-endangering ways in Captain America: Civil War. The feud between him and Steve Rogers stems from a conflict over what to do with the Winter Soldier. Captain America considers him a friend, while Iron Man considers him an assassin mind-controlled by Nazis. Both sides have valid points, and it ends up turning into a fight. So while Cap recruits a team of highly trained soldiers, Stark makes a beeline for a teenage Spider-Man and practically blackmails him into joining his side. Again, to fight a man he's very sure is an unstoppable killing machine.
To make matters weirder, Tony found Spider-Man by spying on him until he figured out he was secretly a high school kid from Queens. And since he's obviously collecting intel on metahumans, he could have just as easily gone one borough in any direction and recruited a ninja lawyer, a superstrong private detective, or an invincible badass -- all of them full-grown adults.
"I'm here to talk to you about the
So yes, any nerd knows Spider-Man is the best hero, but as far as Tony knew, Peter was just an awkward teenager with potentially awesome abilities. Of all the choices, why pick him to go up against history's greatest fist fighter and a Nazi cyborg assassin if you're not specifically trying to watch a child die?