Portrait Painting Canvas

Here is a painting a finished this morning of my son.  This is a portrait painting using acrylic colors on canvas.  I really like the way it turned out--but there are some areas that need word.  The lips are sticking out to me like a sore thumb, and not sure why.  This is my 3rd painting and 1st portrait.  Any comments, hints, or tips are greatly appreciated.

For some reason my kids think he looks like a grown up in this painting but I don't see it.