Bambi is a movie that I approach with some trepidation. My kids and I love the friendships developed in the story. Flower and Thumper are great characters, and Bambi is endearing as well. However, I have had to fast forward through the sad parts for my 3 and 5 year olds, if they want to watch it at all. It is a very emotional movie, and my little ones are disturbed by the loss of the mother and are scared by the fire and the hunters. They also don't understand why the buck (Bambi's dad) isn't really around for Bambi the whole movie.
Overall, I think this movie is best for ages 6 and up, and it's one to watch along with your kids to help explain the issues that come up during the show. The reason I believe that it should be PG is simply because of the issues which it raises. In my mind, there should be less G movies out there which involve the death of a parent, which is such a prevalent theme in animated Disney movies, both old and new.