I'm not sure what credit you're talking about because there isn't one by that name. If you received a $4,050 deduction for the dependent, that's a deduction that only lowers your taxable income, meaning you owe less tax.. It doesn't pay you any money in your refund. Same with the child tax credit, which lowers your taxable income. After that, the tax you owe is calculated on your income and the amount you had withheld on your W=-2s is subtracted. If you did not pay in enough, you will owe at year-end.
This is a very common situation for a married couple because each of you have tax withheld at a rate that assumes you'll each receive a standard deduction for being married. When you file, though, you only get that deduction once, so it's very possible to not have enough withheld to get a refund.
If this doesn't fully answer your question, please add more information about your dependent in the comments section.
