Wife and I discussed this already. We will tell the truth but at appropriate times based on maturity level, or when their version of the story is not true to life. Moderation, yo. Within the limits. But I'm sure that plan of action will change with others' influences.
I like watching nature for what it is. Raw awesomeness. Wife will not watch animals killing other animals for survival unless they are insects or spiders. I'll probably still get yelled at for letting the little ones watch raw nature docs, but at least they will know the truth.
Soon the wild will no longer exist, and all these nature docs will almost be like a fantasy. Might as well see what the world is before we finish shitting all over it.