Last year my wife and I overplayed taxes by a large amount and while it was nice to get that refund we would have preferred to pocket that money directly. We have always filed taxes married filing jointly. My question is how do we fill out our w4s. We have two children (we get the child care tax credit) and she makes significantly more per hour, but if my new job involves lots of overtime then I will be making more than she does. I don't mind overpaying a little, but want to minimize how overpaying.

2 ways:

1) IRS Witholding Calculator - broad strokes, estimates conservatively.

2) If you use TurboTax, there's a function that will calculate a new W4 for both of you.  It can come up with some pretty weird results, like you filing "Married, 6 exemptions" and her "Single, pay an extra $25 per month", but it looks at how much tax you actually owed last year and tries to match that using the IRS's weird math.

You need to increase your allowances on the tax forms you fill out for your employer.

I give myself 8 allowances and it should make my tax owed/refunded close to 0 at the end of year.

Since you have kids, you should put in more allowances than me probably.