[Skywalker]

Rev has some very good advice. I would simply add, find something that motivates them. Punishing behavior has little effectiveness. Rewarding behavior you desire is more effective.

If they like stickers (usually children 3 to 6 years old) start giving those out or give them a star or sticker on their Chore Chart every time they complete a chore.

Older children like collecting cards (Baseball type cards). Every time they complete a task, pass out a card. My children had sticker books and later collector card books. They jumped through all kinds of hoops to get items for their collection (my wife found that cigars work for me )!

Or give them points. Track the points, after so many points for completing tasks, take them for a special treat (ice cream, movies, something they enjoy doing)!