Now to have 3 different stories still I could have the boy observe the death of his mother and be influenced maybe by information she has shared with him giving that more focus and this keeps perspective anchored but changes perception?

I believe you are correct. For example, if you were to concentrate only on the son's narrative of what happened for all three stories, (I'm thinking of a scenario where the son initially experiences the event, then recalls it at two later points in his life as he ages), his perspective on the event would most likely remain the same in all three stories, while his perception of it likely has changed to some extent, as the years pass by.

In this case, and since he was very young, his perspective of what happened likely wouldn't ever change, but I don't think it would be "locked" per se. Some other really eye-opening info that he hadn't known at the time, being revealed to him later in life, (maybe his mother's letter to him that he finds later in life?), could possibly affect his initial perspective, if he absolutely believes in that new info, but even then, it's what his perspective WAS, (his point of view at the time the event happened), that would have to change.

His perception of the event could very easily change however, based on even the simplest things, like his own maturation process over time taking place, or his absorption of little gossipy tidbits people who knew both his father and mother tell him here and there, over the course of his life.

A good example of a change in perspective, could take some political ideology, (to which a person adheres), as being a perspective that "tints" that person's point of view politically. When they look at, say, taxes on the people, they see the taxes from the perspective of the political entity and ideology to which they've dedicated themselves, which incidentally, is now their perspective on that issue as well. If something causes them to instead back a different political ideology, then their perspective on taxes is likely to change as well by default.