As soon as F6 is slowing down to set up under the ball, I have ordinary effort. The fact that he decided to let F7 get it makes no difference. He could have caught it with ordinary effort. Regardless of age level, if I see a 10 year old setting up under the ball like this F6, I have ordinary effort and IFR invoked.
Odd play, but it met every criteria for an infield fly. The umpire didn't declare the infield fly until the infielder was set under it to catch it (which is what is considered ordinary effort).
In my opinion, he could have not called the IF also. The fact that the ball wasn't caught would have helped 'justify' that decision. It wouldn't necessarily mean that not calling it would have been correct. But when the Cardinals would be complaining about it not being called he could hang his hat on it.
I'm most disappointed by the so-called fans in Atlanta. Anyone that throws something from the stands is an idiot. Roll the tape and identify the criminals.