Here's my take on it, for what it's worth. One of the "job descriptions" children have is that their playing leads into learning to work. So it's not unjust or unreasonable to let your children help you. That word LET is used for a reason. I remember once reading the statement, "Children like real things to do. They need to know that they are more than caged pets." (But I don't remember who wrote it.)
Your younger one won't be much in the way of actual help, but a child of that age can pick up toys and put them in baskets, pick up clothes and put them in hampers, and sort of make up a bed. A nine-year-old can learn to wash dishes by hand, put away the dishes if they go in places he or she can reach, sweep or mop, and do a number of other things that don't involve complex equipment.
Just as with school work, house work needs a good attitude and you'll need to model this to your kids. If you don't know how to teach them to approach work with a positive manner, as if it were a game, head over to the library and pick up the old Betty MacDonald book, "Mrs. Piggle-Wiggle." You'll get some good ideas from it.
However, keep in mind that they won't do the jobs as well as you do. When your children do their work you need to encourage effort and improvement and not be too critical. Children are usually glad to help their parents if they know they are really helping and aren't beaten down by negativity. And they will still have plenty of time to play!
For the rest of the work you can't do, you might want to ask your friends and neighbors for the names of people who clean for a living or teens who could come in and do a blitz-clean one afternoon a week. For those people you pay money, of course; for your children's work, you pay in praise, love, hugs, and any extra attention you can give them. :^)
(I just read the other answers, and they're great! Let's hear it for moms!)