The fee seems fair. You're traveling with more stuff, which requires handling through the baggage system - as a result you pay more. If I'm going on a business trip that requires hauling a bunch of junk along that will need to be checked, it's a reasonable expense to assume. The baggage fees are still cheaper than shipping. I'd much rather they not raise all ticket prices across the board to try to keep profitable - baggage fees charge travelers for the services they use.

Kids, as long as they have their own ticket, get their own carry-on allowance. Most of the time I traveled with my mother as a kid (which we did a lot of), we rarely checked baggage and it never seemed like it was difficult to avoid doing so. Besides, most gate agents look the other way when people haul on loads of kindercrap, and they can choose to board first as well and take lots of overhead space.