Molecule Kid (real name Aaron Reece) is the son of Molecule Man.
Not much is known about his past, but he is the teenaged son of the supervillain Molecule Man, who the Avengers have defeated and sent away. He came to town with his father's wand, claiming it was the only thing left for him. Hawkeye and Black Widow were looking for Molecule Man only to encounter his son Aaron who was being targeted by A.I.M. when he was in the possession of his father's wand. After ditching A.I.M., Aaron went the run with Hawkeye and Black Widow in pursuit. Aaron considered the Avengers and A.I.M. the same as they both wanted his father's wand.
Things got worse when the Super-Adaptoid arrived and captured Aaron. Captain America came to Black Widow and Hawkeye's aid and they tripped Super-Adaptoid upon Falcon's arrival. While Captain America and Falcon fought Super-Adaptoid, Black Widow and Hawkeye tried to reason with Aaron until Iron Man arrived. The wand was accidentally broken causing reality to be broken. When Super-Adaptoid attacked, Aaron used the wand's fragments to defeat Super-Adaptoid and undo the damages with Iron Man's help. The others shut down Super-Adaptoid. Aaron was then given to Nick Fury to put in his training program for teenage superheroes.