If you have experience with Flylady, you know that clutter can't be organized. On the other hand, you have children, so there will always be some clutter.
You might try this with movies: ask one family member to go through all of them and set aside any movies that person can't live without. Then ask the next one to do the same thing. Add those keepers to the first keeper pile. Go through each member of the family, including you. When you're all done, there might be some movies left over that nobody can't live without, and those are the ones to give away to other people who would enjoy them.
Sometimes this can work with toys, too. There are really toys that should stay, and perhaps the ones that don't make it into the "love" pile should be allowed to go where they *will* be loved.
Anyhow it's worth a try.
I have to tell myself every day that I love my house and I appreciate the space there is in it. I need to respect that space by not letting it get cluttered up with things we don't use. And I'm much older than your family!
If it'll make you feel better, I'll tell you a family story. My mother, bless her heart, was a first class packrat. She wasn't a hoarder, but she did have a bachelor's degree in clutter. Sometimes she would go through things and realize she didn't need them - but, even though she knew what charities could use them, she couldn't manage to take them there. (She went through the Depression, so she had some of the mentality of "We might need this one day and not be able to afford to buy it!") Soooo... she would pack all the things in boxes, spend the money to UPS them to me several states away, and write, "See if you can use any of this!" And I'd take what I needed, and then I would be the one to give the rest to charity! One does what one can!