W4 questions and Federal withholding

I am married and have 3 small children, when I started my job last year and filled out W4 it came up with me having 7 deduction allowances?  I am now wondering if this is correct as no federal tax is deducted from my check and just a $1.52 for my SC states tax biweekly.   I earn $21/hr and approximately 32 hours a week.