In my opinion, this isn't the kind of information you want to disclose. Most shops won't ask about it. You don't want to raise a red flag unnecessarily. Leave it unsaid unless you need to do otherwise.
On the other hand, you do want to learn about the company culture as it relates to a family-friendly environment, overtime requirements, weekend/night work, etc. You need to see if they meet your needs. That sort of thing usually comes out at some point during your interviews, often when talking with an HR representative. If it doesn't you'll need to find some way to approach the question.
In my shop, our culture is very family-friendly. I allow people to work from home when they feel it is best (perhaps due to childcare issues), and allow them a lot of flexibility in regard to when they arrive at work and when they leave. It works out well for me to arrive before 7:00 AM, and usually leave by 5:30 PM. Others like to arrive after 10:00 and stay late.
If the family-friendliness isn't clear, you'll need to ask. You don't want to be in an environment that isn't a good fit for you and your family. And the employer doesn't want people who can't work the style they require either. Interviews are all about fit - on both sides.