The Sicily bit of your trip sounds exhausting, particularly with 3 young children. It will take a while to get from Pozallo to Taormina and back and that will cut into your sightseeing time.
Re Gozo, you can take your hire car on the ferry but most people don't advocate driving on Malta. You could always collect a hire car on arrival in Gozo. Captain Morgan tours offer a day trip to Gozo in open top jeeps - they sound like fun. Check out their website for more info.
Kay

Kay, Thanks, I'll check it out.

There are some (amateur!) pictures of Malta here: http://community.webshots.com/user/missalg if you'd like to show the kids a bit of where they'll be!

Amy - Lovely photos! Are you sure you're not a professional photographer? I can't show the kids as they are already in Greece, but I can tell you that my mouth is watering to get to Malta! thanks.