I wonder what Mary got for Christmas.

Kay would naturally be in charge of purchasing Mary's gift; and I believe she would ordinarily be responsible for buying Anthony's present too, since holiday planning and child-tending were the domestic purview of the wife in 1950s America.

The fact that Michael has taken the responsibility for Anthony's gift (and delegated it to Tom instead of Kay when he was otherwise occupied) illustrates Michael's patriarchal thinking. As son and heir to the Corleone empire, Anthony has been singled out for special treatment and, by intention at least, a particularly close bond with his father.

Surrounded by father Michael (when he's not away on business), surrogate father Tom, and Michael's button men (Anthony's only "friends," as declared by Kay in the later abortion confession scene), Anthony is groomed to be a man's man in the male-dominated world of power, whether criminal or legitimate (and the line between the two is often blurred in GF II).

This is not to say that Michael's only motive for close involvement with Anthony is to prepare him as successor. I believe Michael has genuine love for his son which gives his more selfish ambitions a purifying undertone. Perhaps deep down, he wants what all fathers want for their sons: to be proud of him, to have dreams for him, to inspire confidence in him, to see a little of himself in him. It's one of the tragedies of the film that by emulating and respecting his own late father, Michael gradually becomes a stranger to his own son.