it is narrated from the point of view of a child entering adolescence,
This is called a "coming of age" narrative and it is quite common and can be quite good. In this particular film I suppose he was forced to grow up pretty quickly, but that doesn't change the fact that he went from being dead instantly without dad's help, to basically becoming Rambo a couple of days later. The whole killing, then boiling, then placing the skull of his mother in an advantageous position.... rather than, i would imagine, spending as much time with his mother as possible before she died, would have made more sense to me. I guess they need it for the story.
it was also a bit strange that mama went from not being able to get out of bed or even really move very much, to running around and even killing one of the fat zombies while her son was asleep.
It's fine that you liked it, I am not trying to say you are wrong or stupid because you don't think what I think...we all have our differences and preferences when it comes to films but for me this movie was just an abomination and the most disappointing theater ticket I have purchased in many years.