Okay, I know your little one is just 6 months old, but some of these have lovely music and soft narration, so they might just capture his attention. Bonus, you'll like them, too!
They are not aimed at children (well, except for the National Geographic Really Wild Animals series, but where is it written that you have to only show children's images to children?) but there are certainly images that are eye-catching!
I would recommend the ones I highlighted in colour. Our ds (age 7 1/2 years) has been watching these since he was just a little munchkin (watched Walking With Dinosaurs at age 18 months!).
If any of these sound too much for you, what about Kipper or Franklin or Little Bear?? All nice, sweet and gentle. Quiet, too!
*Life On Earth
*Life Of Birds
*Secret Life Of Plants
*Life Of Mammals
*Trials Of Life
Jewel Of the Earth (all about amber)
*Life In the Undergrowth (all about insects)
Japan's Secret Garden (David Attenborough)
Garden Of Eden (on the Seychelle Islands)
The Unknown World (microscopic life)
Treasures Of the Great Barrier Reef
Miracle Of Life (in the womb)
The Great Barrier Reef
The Living Sea
Coral Reef Adventure
Blue Planet (different from the David Attenborough series above)
Origins Of Life
PBS Home Video:
Secrets Of the Ocean Realm
Walking With Dinosaurs
Walking With Cavemen
Walking With Prehistoric Beasts
Chased By Dinosaurs
When Dinosaurs Roamed America
Any of the Really Wild Animals videos (set of 10 available, any and all are terrific for kids AND adults!)
Any National Geographic specials