Understanding of what is happening is often very limited. When I read books or talk to her, I sometimes use words that are unknown to her, she only started asking for the meaning of them recently (she just turned 3). So she will probably only understand 20%-30% even when she understands conversations quite well at home. She is still missing cultural context. She is only starting to understand the difference between a living and a stuffed animal.
In an animation movie somebody might hit somebody else, which appears funny to an adult. A child might just take this as normal behaviour and repeats it the next time she sees somebody and doesn't understand why it's not funny.
Understanding the real world is difficult enough for her.
But that's an issue with the content, not the medium, right? There will be shows geared exactly towards kid that age that teach them the right lessons.