The kids have defined the Mets’ and Yankees’ seasons.

And the two teams, who are set to begin the latest round of the Subway Series on Tuesday night at Citi Field — Max Scherzer starts the opener against Luis Severino, and Justin Verlander and Gerrit Cole square off Wednesday — have reversed courses since the start of the season in what they’ve asked and expected out of their youth.

It’s not necessarily positive in either case, but examining the Mets’ and Yankees’ first- and second-year players reveals larger trends about the teams’ outlooks.

And perhaps each team’s ultimate flaw.