I didn't prepare well for Advent this year. In the past we've had an Advent wreath with our own candles at home. We've had interactive Advent readings to do together as a family each evening. I know some families buy the advent calendars that have a little gift behind each day's window. I remember a homemade advent calendar when I was young--I think it just had something like lollipops tied to it. The calendar's aren't always very meaningful, though. Often they just add more sugar to a child's diet--or more trinkets that they probably don't need.
I was given a book a few years ago, Seeking the Christmas Lamb: Forty Days of Celebrating Christ's Sacrifice Through The Season by Tamara Buchan, that I may try and use this year. Most Christian bookstores will have some Advent devotionals. Check with your pastor or priest, too. If you want to make Advent more impactful and less about materialism, be sure to check out Advent Conspiracy. Their resources page has a download for a children's ministry curriculum.
One easy-to-access online resource we've used a few times is The Jesse Tree. It has short daily readings, a question for reflection, a prayer and a picture with which to make a mobile.
May you find something memorable and meaningful for your family.