The withholding is correct if you entered married and one child on the W-4. Your main issue is if your spouse also works and also claimed the child on the W-4 with married ... then you could be underwithheld. In that case the person with the lower wage should fill in a new W-4 and choose the SINGLE option and do NOT enter the child OR try to fill in the impossible 4 page W-4 worksheet to come to the same conclusion.
