Donna,
I haven't been diligent in following all of your detailed postings. My apologies.
But just read the suggestion that the small protrusion of the crop might have been caused by casting (pellet) materials in the crop, not food.
Not so, by any means. Castings never cause the crop to protrude; only ingested food will do that. The birds had fed, doubtless.
--John Blakeman
John, many thanks for the clarification.  Do the leftovers go down further than the crop before being expelled?  Or are they just too flattened from being worked over that they don't show?  Or ?
Also know,  many will be relieved to hear that these fledglings did eat something on Sunday. 
JEFF JOHNSON HAS BEEN DILIGENTLY TRACKING CENTRAL PARK FLEDGLINGS WHILE I'VE HAD INTERNET ISSUES SO STAY TUNED FOR MORE POSTS TODAY!  WE'RE GOING TO CATCH UP!!!