Organized tours are available. Wedding in Rio Varig Brazilian Airlines suggested consolidators for low-priced tickets. American Airlines Group Sales Desk said for every 20 tickets you buy, you get one free. It's pretty much a matter of policy that they'd have group rates. Best Western also has a couple hotels in Rio.
Children are welcome on most tours.
The naturalist lecturers aboard the ships work hard to keep kids entertained when they're in the audience. You'll have to fly to Ushaia, Argentina to hop aboard the ships. Most of them are converted Russian research vessels and hold under 50 passengers. Take seasickness medication with you. Ships go through the Drake Passage, considered to be the roughest seas in the world.