I brought a printout to our daf yomi shiur of your berachos 48 paragraph 2 (The Obligation of a Minor in mitzvos) and the question was raised, what do you mean by your statement that a minor may recite Birkas Ha"Mazon for a person over the age of Bar Mitzva if that person ate less than a k'Zayis of bread. I assume you don't mean less than a k'zayis but rather less than kedai sviya, and so too one would have to amend your answer accordingly.(One who ate less than a kezayis doesn't have to Bentsch). Perhaps you meant something entirely different-am not sure. Thanks