In the end of the movie they sing the Frankie Valli and the Four Seasons song "Walk Like a Man". In the scene where Shakes is in Carol's home (at around 1h 17 mins) he is picking up a record from the shaft of that same single.
The flag of Greece being displayed on the hot dog cart when the boys try to steal it was only adopted by Greece in 1978. At the time of the movie, the flag of Greece was made of a single white cross on blue background.
Author Lorenzo Carcaterra has claimed that his book on which the film is based was a true story of his childhood. When the New York legal community went on record stating that no cases resembling the events of his book could be found in any court records, Carcaterra refused to discuss the discrepancy. His claims have been neither proven or disproven.