These are appropriate for all ages. David Attenborough narrates and costars (nature being the star...:)):
Life of Mammals (BBC) These are wonderful nature studies. David Attenborough has such a love for nature and the way creation works together, though he does not put it quite like that. He doesn't harp on the evils of man, either.
The Blue Planet (BBC)
Planet Earth (BBC) The photography is spectacular, but the unique aspect of this set of 5 DVD's is the aerial shots. You get a much better sense of how pack animals hunt, for one thing. Be very careful to avoid the version with Sigourney Weaver as narrator. She can act, but she cannot narrate.
The Living Desert (Walt Disney) This is an older documentary which personifies the animals one views. It's both entertaining and informative.
Amazing Animals series (DK Vision) There are 13 (that I know of) in the series: Animal Appetites, Poisonous Animals, Mini-beasts, Nighttime Animals, Animal Babies, Animal Builders, Animal Journeys, Animal Senses, Animal Survivors, Tropical Birds, Animal Weapons, Animal Disguises, Armored Animals. These are geared to ages 3-7, provide lots of interesting details in an entertaining if somewhat silly format. Our 5 year old son, Will, especially likes the silly aspect. Henry the Lizard is often wrong about something and Will likes the way he's very gracious about corrections. It's also fun for a 5 year old to knooooow someone else is wrong even if he's not sure about the complete truth.