So if you have one child, you get a $2000 credit (dollar for dollar, not a deduction - and it's higher right now because of hte extra bump to $3,600, but for this we will say $2000.
If your company does bi-weekly paychecks, you'll get 26 a year, so it will be a $76 credit applied to your witholdings every two weeks. If it's twice monthly, you'd get $83.33 per kid