For the boys, if there into cars, AND if you're going in April, there's an exhibition going on about cars - some fantastic old-new Ferrarri's on display called: The Legend of Speed, Art, Motorization & Society in 20th century Italy, at the Palazzo delle Esposizioni, Via Nazionale 194 (it's only 12.50 euro tix cost, phone 06 3996 7500. Not sure how long it's to be there, but google it or the museum and you should find the info) Also, Castel Sant'Angelo museum (Lungo Tevere 50, National Museum of St Angelo) has the largest collection of militaria and arms IN THE WORLD, so they might enjoy that, too!
All the Piazza's have nightlife galore for the younger crowds, and Testaccio area of Trastevere is geared toward young, too. But even there you'll find a lot of mixed crowds of both young and old alike. Then there's the Porta Portese Flea Market, Pyramid of Caius (S of Aventine Hill at Porta Ostiense), Forum Romano, Colosseum, etc, or even a 1-1.5 hr train ride to Naples and Pompeii.
Just a few thoughts...
~ciao

