We are a family of women staying a week in Rome. All active. We don't mind the off beat. We have an all day tour to get our bearings and planning a day at the Vatican and surroundings. First time for all but one. Rick Steves has given us some insights but is there something that is a "do not miss" ?
I can suggest two things: The Catacombs of Priscilla are lesser known and have the world's oldest-known image of Mary. We enjoyed our visit and it wasn't crowded. It's in Rome itself, but in a neighbourhood I didn't know, so we took a cab there and back, but we coud have just as easily taken the bus. An day trip by train (1 hr) to Orvieto, a delightful hiltop town, with a magnificent church! A taste of Umbria and Tuscany close to Rome...
Forgot one more!! The Spanish Steps are fun to just hang around and people watch -- lots of young people sitting on the steps. The area around there is full of very nice boutiques and fashionista shops, so it's woud be great for a few hours of window shopping.
The previous post is a great suggestion; Spanish Steps after sunset is the meeting spot for young people. Another suggestion: the Tivoli gardens just outside Rome if your girls like gardens with lots of outdoor fountains including a big one like a waterfall which you can walk behind (W/O getting wet if you're careful). I think it's part of Villa d'Este
While at the spanish steps you will be approached by a smiling middle eastern immigrant. They will hand one or both of your teenage girls a fake cloth rose. The girls will be so happy to accept the "gift". After he hands the girls a rose, the immigrant will turn to you and ask for "a little something" I'm not sure what happens if you actually give him "a little something" I suspect he'll want more. As for me, I quickly returned the rose. Probably the best technique would be to buy a couple cheap fake roses at a 99 cents store and pack them. Carry them around in Rome, or at least at the Spanish steps. Wards off the scammers. My "Aha!" moment came our last day in Rome. Maybe it was because it was the last day of the trip, I'm not sure... The Pantheon is remarkable. To think it has been around 2000 years. ...nearby, the Santa Maria Sopra Minerva church. Has a Michelangelo statue of Jesus.
...then...amazing...San Luigi dei Francesi. This is the french national cathedral in Rome. http://en.wikipedia.org/wiki/San_Luigi_dei_Francesi It's like the French saying "You call that beautiful? I'll show you beautiful!" to the Italians. You get the idea. We stumbled onto this church, and there was a service going on, so we couldn't walk around. The interior is amazing. If I returned to Rome and could only go to one place, this is the place I would go. I ended up feeling that the Pantheon is so remarkable that any churches nearby really stepped up their game.