A little boy punching out flashcards from the cardboard they came in.
A boy punches his new flashcards from the carboard they came i.
A boy is punching out flashcards.
A little boy is a boy as part of the description punching new flashcards (which must be new as being punched from the cardboard they came in).
A boy punching out his new flashcards is synonymous with a boy punching out his flashcards