Make it clear that there will be consequences, either good or bad, depending on how well the children care for their assigned task. Then, either enforce the consequences or grant the rewards.
وأوضح لهم انك ستكافئهم او تعاقبهم وفقا لمدى اهتمامهم الجدي بإتمامها ،‏ ثم احرص على تطبيق ما قلته .‏