2 1/2 days in Rome, Apr 29-May 2/09, with kids, 11 and 13. What MUST we see/do:)?

[dragongirl64]

I really want to maximize our time in Rome and know that it is a city we could spend a lot of time in and not see it all, but does anyone have any ideas as to what is truly a must-see/do with kids? We are staying in an apartment in the Campo de' Fiori area, nice and centrally located. We should arrive into Rome off our 10 day Roman Empire cruise by noon on April 29. I am thinking of heading over to the Colloseum right after we drop off our bags and seeing that (do we need a tour or is this ok to do on our own?) and then over to the Appian Way and hopefully, 2 hour Gladiator School for the kids, (which I have heard lots about, all very positive!), followed by touring some of the Catacombs in the area, then head back to Campo de' Fiori for dinner that night. That still leaves us with 2 full days, which of course includes the Vatican/St. Peter's and the Forum, Spanish Steps, Trevi Fountain etc., the best timing to do all those things, and what we can do on our own and what we need to book a tour for. Any suggestions are all most welcome, including good restos for kids (mine are very good eaters and will try most anything, thankfully!) and what is doable in a day without us all dropping dead from exhaustion!