We took our 8-year-old son to Rome for 4 days this summer. In that short space we crammed a LOT of things that are in all the guidebooks - the Vatican, the Colisseum and Forum, the Pantheon, etc.
"Around Rome with Kids" added SEVERAL kid-friendly sites that we never saw in any other guidebook, including Fodor's big ones. For example:
1) The Archaebus - takes a tour to a park on the outskirts of the city where there are many ruins of Roman acqueducts, and goes right down the oldest stones on the Appian Way--in air-conditioned comfort;
2) The "Plastico di Roma" - enormous scale model of Ancient Rome in the Musselini (sp?) era Museo di Civilta Romana out in the EUR district
3) The Time Elevator - expensive but fun simulator ride near the Piazza Venezia. Cheesy but a good antidote to the seriousness of the ruins.
The best part, from the Mom perspective, is that in addition to hours, prices, and directions to each site, the authors point out kid-friendly restaurants and pit stops nearby. You are never more than a few yards from a decent gelato...