Tip all out and ask kids to put into their own box what they say is theirs. Another box can be made for shared toys. Anything else is gone.
If this seems hard removing stuff, then think about picking up a toy that nobody wants week after week.
A short note on this is for you to remember, that if you get your kids early in life to be tidy, then in theory your future at home should be clearer and less chaotic.
Share your kids cleaning stories, I would love to hear from you.