"He has not wanted to miss the boy's birthday."
Translation:Non ha voluto mancare il compleanno del ragazzo.
When one misses something or someone in the sense that one longs for that something or someone to be near one, then that something/someone is the subject in Italian, not the object. One, on the hand, is in fact expressed as the indirect object in Italian. E.g. "I miss you." Is "Mi manci.", Literally meaning "You are missing in such a way that affects me."
Apart from the "mancare al compleanno" problem I also have problem with the "non ha voluto". And furthermore in English I bet no one would say "he has not wanted to miss...", but rather would everyone say "he didn't want to miss", so if we speak about a non willing to miss anything we would also say in Italian "non voleva mancare al compleanno" - this should be accepted as correct, in my opinion. (Of course I know that in Italian they say "non ha voluto...", which is ALSO correct.
As a native English speaker I agree that you wouldn't say "he has not wanted to miss...". You'd say "he didn't want to miss" or even "he wanted not to miss" (which is technically correct but almost no one would say it that way nowadays). If neither of those fit, you'd have to use a completely different sentence, like "he was worried about missing...".