Ushuaia

Martillo Island (Isla Martillo) - A trip to Martillo Island to see the Magellanic penguins is a must do. Take a day tour that includes a bus ride overland to Estancia Harberton, then zodiac boat to the island. On the island, kids will have a chance to walk among the penguins - they're not afraid of people. September to February, not only will you see the penguins, but also penguin nests (burrows in the ground) and chicks. Highly recommended!

Boat ride up the Beagle Channel - Go for a three hour boat ride up the Beagle Channel to Les Eclaireurs lighthouse. From the boat, you'll see oodles of penguins and sea lions lolling on aptly-named Sea Lions Island (Isla de los Lobos), cormorants, albatrosses, and other sea birds in the air (bring your binoculars).
Tierra del Fuego National Park -
Train at the End of the World (Tren del Fin del Mundo) - Colorful engines pull modern cars on a one hour ride that ends in Tierra del Fuego National Park. The Ferrocarril Austral Fueguino leaves from the End of the World Station (Estacion del Fin del Mundo) in the River Pipo Valley five miles west of Ushuaia. Get off at the Cascada la Macarena station for beautiful waterfalls and reconstruction of a Yamana native village.
Hike in Tierra del Fuego National Park - Easy hiking trails along Lapataia Bay. Look for Red foxes and guanaco, and non-native beavers.