Added: Per your SWH. Okay, here's another thought.
Years ago when my kids watched a show that featured a dog and his boy, in which the dog "talked" as the narrator, (maybe somebody can remind me of the name of the show), the boy couldn't seem to do his math without his calculator. And he was doing poorly in class. He didn't understand the math concepts and was using the calculator as a crutch.
The neighbor saw what was happening, and hired him to work at her yard sale. She sat him down at the table and told him that she would give him 10% of all the sales. If my memory is right, he was to give people a 5% discount if they bought over a certain dollar amount as well. He was excited, but realized that he didn't have his calculator. She told him that he had to do without it. He struggled at first, but by the end of the day, he was doing the math right. (No one was going to let him "wing it" about their discount! And he couldn't stand to wait til the end to see how much money he was making.)
After it was all done, she talked to him about understanding concepts instead of relying on his calculator, and how doing something that really USED the math would teach him how to do it. It's kind of like giving a 15% tip when you go out to a restaurant.
I loved that show - it wasn't just about math, but about history and science, etc.
The point is, find some real life ways to use math. Do "field trips" where you measure things, figure out word problem stuff in real life, etc. And I really mean it when I say, don't allow them to down themselves out loud about their math skills. They are creating a self-fulfilling prophecy if allowed to.
Lastly, do you allow them to play other computer games or Xbox or gameboy? If you do, put a moratorium on that. Tell them that either they do the computer math games, or they do nothing. They have to earn electronic time by doing the math games and not complaining. You hold the reins to this, V.. USE THEM!
Original:
Try a computer program (CD) that teaches math through fun interaction. (Dorling Kindersley - DK - is a great start.)
My kids did several of those programs. One of them had them looking for treasure and they were absolutely hooked on it. They did one that taught grammar too.
If I were you, I'd say everytime you hear it come out of their mouths "I don't want to hear it. If you complain again, you're going to clean the toilet" and then show them that you mean it. Either they'll stop saying it, or you'll have a clean toilet!
Dawn