Like some of my friends below have said, be sure that your child has down time before jumping into homework. Also, break the homework into small chunks so that it isn't an overwhelming task. At school, we frequently take 'brain breaks' to get us moving and get the juices flowing. Have your child take mini brain breaks during homework time. You might say "Stop! 10 jumping jacks . . . ready? Go!" or maybe say "Freeze! Do the Twist! Ready, go!" You can use a song, activity, exercise. . .whatever!
Another great idea. . .have a special place for doing homework. A special desk with school supplies would make anyone want to do their homework! Who doesn't love school supplies???