OK folks, I need your help. Here is our proposed itenerary. It's for two adults and two kids (8 & 10). I'm trying not to pack my days and avoid overload. So here goes
Wednesday-Arrive Rome late afternoon.
Thursday & Friday - Vatican and Coleseuum
Saturday-Fly to Palermo, get car and drive to Montreale. Eat pastries. Overnight in Erice.
Sunday& Monday- Stay in Erice, eat more pastries, visit Selinute or Segesta and/or Agrigento
Tuesday-Rest
Wednesday & Thursday-Syracusa or Stromboli
Friday-Fly to Naples, Eat pizza
Saturday- Pompeii or Herculaneum
Sunday-Fly back home

Some specific questions

How long does it take to get to the Naples airport from downtown and how far ahead do we have to arrive to get our plane? Instead of flying to Naples should we take the ferry? Thanks for any ideas.

I like your eating agenda. Don't forget gelato!

I would give yourself an extra day in Rome if you have never been there. You seem to dedicate so much to Sicily.Is that what you really want? 3 days in Erice seems long.Taormina would be nice did you ever consider it? 2 hour drive from Trapani ( close to Etice) and Catania airport near Taormina. Your rest days - do you have a hotel with a pool or something to entertain your two children? Once you do Naples did you consider Sorrento or Capri? Kids might like it. Just ideas. Good luck.

Your trip sounds great. I'm a little confused about a couple of things. You ask how long it takes to get from downtown Naples to the airport (the answer is a about a half hour by bus from the train station) but earlier you mention flying from Rome to Palermo. Are you planning to go from Rome to Naples and then fly on to Palermo? If so, this sounds like a very long (and unpleasant)day.You can fly directly from Rome to Palermo on Air One (http://www.air-one.it)for about 45 Euro per person.
Even with a direct flight, I think you are doing way too much if you are planning on flying into Palermo, renting a car, driving to Monreale, touring the cathedral and then driving on to Erice in time to get a room that night. Why pay the higher price of a room in Erice on the first night if you are only going to crash there? You might want to consider spending your first night or two in Palermo instead. Segesta and Selinunte (both worth seeing) are close enough to Palermo for day trips. Palermo, itself has many attractions, including the Sicilian puppet theatre: (http://www.bestofsicily.com/mag/art29.htm.)
I also agree with the others that three days in Erice (particularly with young children) is too much. Erice is beautiful, and definitely worth seeing, but it's small and you can see the whole town in a day. It is situated at the top of a very steep hill and I would think you would be pretty much stuck there for the night because I don't think you want to drive back up that road at night. I'd look at another town, perhaps Porto Palo or Sciacca, to spend a night. It's on the way to Agrigento from Erice and you could continue on to Siracusa (although that is a long drive after having spent hours walking around Agrigento.) Finally, Siracusa and Stromboli are nowhere near each other, and combining the drive from Siracusa to Milazzo with the ferry ride from Milazzo to Stromboli, you are going to kill an entire day. Why not stick to Siracusa, or head up the coast to Giardini-Naxos or Taormina? You'll be close to the Catania airport and can fly to Naples from there.
Roger

Thanks for all your input. I have been to Rome a number of times and while I love it, my travel partner does not so we are keeping it short. He also really wanted to see Sicily. (Which actaully turns out to be a lot more interesting than I would have thought!) We are flying from Rome directly to Palermo. On the way back we fly out of Naples. My only reason for staying in Erice so long was several posts and books stating how good the pastries there were (food is a major theme of our trips!)If anyone has ideas on other good pastry places please pass them on.. Finally we can't decide between Stromboli (how often do you get to see a live volcano?) and Syracusa. Eventually we will have to decide. Thanks again