Many of us are more productive when we are working within a prescribed framework. That's why it's so important to set and keep a schedule when working from home. If your job requires a lot of interaction with the folks back at the office, you should try your best to align your schedule with the normal nine-to-five. If your work is largely independent, you have the freedom to work earlier or later than the regular work day, or split your day into several shifts.
If you have a spouse and kids, it's even more important to set a firm work schedule. Every week, sit down with your spouse to chart upcoming doctor's appointments and soccer practices, and to assess each other's workload. Devise a schedule that shares parental duties while giving each person enough time to realistically get their work done.
Print out the weekly schedule and tape it to your office door. By Tuesday, your toddler will have ripped it down and drawn a 20-legged elephant on it, but a schedule's a schedule. Stick to it.