My 3 yr old is really smart and I just didn't like when the penguins were singing their unique heart songs to find a mate some of them would bump into another penguin's private parts. There were also references to male penguins not wanting to hug each other. And then some sexual innuendos from a male penguin about other female penguins wanting him. It was fine for my two older children, but I took my 3 year old to see it and I would not particularly like to see her imitating the way they were dancing (bumping private parts). You'd have to know my daughter to understand. She is beautiful, the center of attention everywhere we go, she sings and loves to dance - and it is not a stretch for me to see her imitating the dancing she sees.
With Shrek I felt the sexual innuendos were adult enough to fly over the younger ones heads so to speak. But I didn't care for the language at all. We don't cuss and neither do most of our friends. But we are are more of an influence over our children than a movie is. And I felt with Shrek that the overall message was too good to pass up. When the bad language took place we just used that as a learning tool. We discussed that even though movies and other people may say cuss words that doesn't mean that we have to follow suit.
It all works out. I didn't dislike Happy Feet, I just was a little disappointed after all the hype about it.