"In this country, we are apt to let children romp away their existence, till they get to be thirteen or fourteen [or twenty-three or twenty-seven]. This is not well. It is not well for the purses and patience of parents; and it has a still worse effect on the morals and habits of children. Begin early is the great maxim for everything in education. A child of six years can be made useful; and should be taught to consider every day lost in which some little thing has not been done to assist others."
-- Lydia Marie Child, The American Frugal Housewife.
Even 1- and 2- and 3-years-old. As soon as children start crawling, have them come and go where you direct. Teach them to help you by staying where you put them, in a particular area (on a blanket, on a rug, in a room with you), or by following along with you as you move through the house. If they understand the mental and physical coordination of crawling or scooting, they likewise can understand related commands: stop, go, come, stay.
Move from those simple ideas to teaching them how to pick up their toys and put them into a box or basket. It's good for their muscle development; it is essentially a developmental game for them. Work is play and play is work for our tiny children. They are exerting energy and thought, analyzing, memorizing, whether they are "playing" with a stack of blocks or "working" at putting them away. Don't let your own cultural, adult-sized concepts of work (e.g., that it's not fun) get in the way of your children learning and growing.
Love work, and so will they.
Children will only despise work if you teach them to do so. That work is difficult, uncomfortable, or undesirable will not occur to them unless they read so on your face and hear so in your voice. If you greet your own day's work with eagerness, joy, a quick hand and a creative mind, they will approach it in the same way.
Decide now what kind of attitude you want your children to have in 5, 10, or 15 years. Would you prefer to nag at an unwilling, complaining, complacent teenager, or have the help of a young adult who deals with his duties as a pleasant and necessary course of the day? Choose the attitude and cultivate it in yourself. Your daily example is the most powerful tool of training helpful, happy, hard-working children.
Bring your children close to you.
Don't banish children to play rooms and toy closets. They want you, and they want to learn from you. Certainly there are times when they can and should entertain themselves; but there is such wealth of opportunity to teach and train as you do your own work with them alongside. Don't lose your opportunities for the sake of shaving a few minutes off each task. The tasks will always be there, but the children will grow and leave. Save super-efficiency for the time when they are grown and gone.