there is two different types of tax credit.One for if your not working which is child tax credits.You are not allowed to work and claim this.I think your allowed aboout �20 a week extra but any more then you must declare it.And there is working family tax credits which I think has changed its name.But if your working under 16hrs a week can claim.If you working 16hrs or less you are considered as working part time.Make sure you are on the correct one because YOU are respponsable and may have to pay it back if you have been overpaid.I believe it would be seen as fraud if you don't