I wonder how old you are. Judging a five year old child (even in a movie..especially in a movie)..is kind of funky.
This is an animated movie with a broad spectrum of emotions dispersed throughout the scenes. It is a family film with children in it (who would have thought right?)
It has a child in it that is from another world..a child that is excited about everything. A child that has an eccentric personality and that is ok because without her and her personality there would be no movie.
I personally feel like two different types of parents and "worlds" were compared. The father has a ton of children and they live in abundance of all sorts of resources yet his child is "selfish" like you say. The boy and his mother live in a modest and small home, yet he is a quiet and reserved to a point boy.
Haven't you ever had a friend that you traded presents and promises with? I think you took the "commitment" too seriously. Children say things..did you know that?
Of course you are allowed to have an opinion but..I'm sure you have some traits even in adulthood that, if we saw, we would think are annoying too. ^-^

i just hope that you don't have a daughter.

Ponyo is a little girl. Little kids can be annoying. This complaint makes no sense

Agree so was so full of herself and I found her kind of ugly and hated her voice