How Can I Get My Work To Understand I Have Kids??

Having kids can be a stress on work sometimes.  Kids should never come second to the job, but you have to have the job to support the kids.  How do you deal with the boss who doesn't understand when the kids get sick or you need to have time off to take them somewhere?  What discussions can you have to make your boss understand that your work won't suffer just becuase you have kids, too.