There is a number on your summons that you can call. Even if you have already postponed you are not expected to serve when you are a caregiver of small children or anyone for that matter. Call that number and they will tell you exactly what you need to send in (i.e. copies of birth certificates of your children, etc.) I literally just went through this a few weeks ago and was dismissed before I even had to serve. The woman who helped me was very annoyed that anyone had suggested I even needed to show up.
Also, when you call, make sure they do not insist you come into the office to show "proof". You can do this all by mail.
Best of luck!