S.S.
More than chores, more than modeling, is working WITH your children. Children can watch you slave away all day long or forced to work by themselves will learn to cut corners. Do it together (yes, it takes 4 times as long, but you're teaching, not getting chores done).
I had a friend with a downs syndrome son, who was told what he could be taught when to fulfill his potential. I was amazed because most "regular" kids don't do things at that age. So I followed her schedule.
My son was about 2 when he started "helping"-he put the clothes in the washer, poured in soap (once I filled it), turned the nob, etc. He put dishes in the dishwasher (I rinsed and told him where they went), put in the soap packet and turned it on. I have separate laundry baskets for whites and colors. He was about 2 1/2 and came to me worried because he didn't know where to put his tighty whities with blue sail boats.
He has always worked with me pulling weeds, scrubbing bathtubs, mopping floors. He has used power tools to build a club house.
He's 10 now and still has his moments when he doesn't want to do it, but when he does, he does it completely. I can trust him to handle any home appliance or item in our home (even my china). I joke that next week he'll be moving out on his own, because he's so self sufficient.
We've had other kids live with us-my nieces, friends kids, foster kids (all different ages and levels) and I work the same way with each one. They may not like to work, but they know how, and they know that I care about them enough to be right there with them working too.
Good Luck.