I'm pretty positive that the skull kid who gave you the piece of hearth in OOT is the same in MM. Like blackice said: he said something in the ending like "you smell like the forest kid who taught me that song".
but just to be sure, i looked on youtube for the MM ending:
he says that line...
yeah mases made a good point there about TP. it didn 't cross my mind.
yeah there were more then one skull kid. but at the end skull kid said somthing like: "you smell like that boy who taught me that song"
so then i assume he is the only one who know saria's song among the skull kid 's
Now i have been wondering, the skull kid that gives you a piece of hearth when you play saria 's song in OOT is the same skull kid in MM right?
and in OOT it was explained that kids without a fairy would turn into a skull kid and normal persons into a stallfos. either way they always wonder...