They are 5 & 7 years old, they should know better, by now.
The book: "Have a New Kid By Friday" by Leman... has some really great tips and suggestions. Not 'mean' solutions... but useful and works.
You can get it from Amazon or E-bay.
I recommend it.
Its an easy quick read.
Buy washable markers and crayons. Crayola makes them.
Tell them to clean it themselves.... and you right there, and show them how to clean it....
Make them do chores... they are old enough.
Make a poster, and list the "rules" of the home.
Teach them what a "family" is... and how they are a PART of that. They are not separate. You are not their maid.
If my kids break something or lose something, and they know better, I do not replace it... and they just have to deal with it.
gather up all your kids things/toys/anything... and put it in a closet. Put EVERYTHING in time-out. Or leave it there indefinitely. AND then have them, if they want something from the closet, earn it. Or have to ask for it POLITELY... and as soon as they are done with it, put it back in the closet. Have them play with anything, ONLY in 1 certain room. ONLY.
LET them get bored, with NONE of their toys/markers out. Too bad.
Tell them, to read a book.
Leave the books out for them.
DO NOT GET THEM anything else, new.
Or go to the 2nd hand store ONLY... to get things, if anything. It will be a good lesson.
My kids are only 3.5 and 7 years old, and we have taught them the value of money and that everything costs something, and has "value."
Teach your kids that.
And in school, at their ages, your kids are taught about "money" already... right? and addition/subtraction of it and how to 'pay' for things.
good luck,
Susan