S.L.
I don't really have any advice for you, but I'm right there with you. I feel like I should be doing a better job, and my husband has serious issues with clutter. He's obsessed with not having clutter or mess anywhere. Once he said he'd like our house to look like no one lives here. So I've got a lot of pressure.
The one thing that really helped me from FlyLady is her 15 minute timer trick. It works for kids, too, although 15 minutes may be too long for them. My kids are really young (5 & 3) so 10 minutes is good for them (it usually takes about 5 minutes for them to actually start cleaning, so I only expect 5 minutes of cleaning.) We take a break from playing to clean until the timer rings. Then we can play again.
Another thing I tell my son when he feels overwhelmed with the amount of things to clean up is to pick up 5 things at a time. I also have him pick up five things when he goes to his room to put on his pj's or get dressed each day. 5 things is so manageable that he rarely complains.
It also helps when we want to do something or go somewhere, but things are really messy. If we want to watch a 2 hour movie, and it's 2 hours and 15 minutes before bedtime, I tell the kids that we have to clean up the family room before we can watch the movie, and we only have 15 minutes to do it, or we'll run out of time to watch the movie. They usually scamper around cleaning up as fast as they can.
I've learned that kids don't clean much alone. They want to be with you and spend time with you. And they don't have the skills to tackle a big mess on their own, so they get overwhelmed. So as hard as it is, you'll have to join in. DON'T get suckered into doing it all, though. It sounds so simple, but just yesterday I had a brilliant idea that worked. If you say you'll pick up half the mega blocks, take turns putting them away, or they'll watch you put away half, then complain about putting away their half. I don't know why I didn't think of it before. I did it with my 3 year old. I said, "I put mine away!" and he said, "here's mine!" and we were done in record time.
Another fun thing is to play "basketball." This only works for certain toys, that aren't fragile and belong in a large bin. We have fun tossing MegaBlocks into their giant bins and seeing who can make the most "baskets."
Thanks for asking the question, because I've sort of forgotten about all these tricks I've tried. I have way more things in my arsenal than I thought! I'll have to try them out again today.