In case of successful and registered employment families are entitled to certain allowances. To ensure this one of you have to work minimum 18 hours a week! The government defines a minimum amount which is necessary in order for a family to live a normal and financially secured life. If the amount of annual family income is less than minimum, it complements the working (child tax if you have children) tax credit and child benefit.
If you apply for child benefit and you get it paid, you have to cancel the benefit abroad. If you do not do it and you get caught, you have to pay the cheated amount back in both countries and you might have to pay a penalty charge due to your undeclared period. -You must report any kind of change in your circumstances to get your payment continuously. In case of failure to notify they can void the regular payment to you.