It is quite possible that they find that they do not have time for homework. Sit down and draw up a time schedule with their help. Remember it is imperative that the decisions be theirs. Do not impose your viewpoint on them. Self-imposed rules are easier to stick to and a person feels bound to stick to them.
Rules made by someone else on the other hand seem unjust and feel like a burden.
Your own experiences will validate the truth in this. Let them set a deadline for finishing homework everyday, and also a punishment if they do not. This will be a challenge to them and at the same time they learn to be responsible for their own actions. So they are not just doing homework but learning important life lessons as well. Guide them in choosing activities with which they fill their day.