[monksy]

If each kid has a ticket, you can check a bag under their name. Why do you need 2 bags?

[namiller2]

As in, if they had to pay to check bags, they would bring them all as carry on, where with southwest they can check them for free and not deal with. I'm not paying to check bags either.

[mikeash]

I'd guess they're comparing against airlines that charge for all checked bags starting from the first one, rather than airlines that give you one for free.