We are just back from Rome, we took our 3 kids and we had an amazing time - my heart is still there! The bus and metro cost is ?1 for a single fare, very cheap. Rome is small enough to walk around, the only time we used public transport was to go to the Vatican Museum & St. Peter's. Be careful if you take the no. 64 bus to the Vatican, it is pickpocket heaven. You buy the tickets for the bus in the little tabacco shops, and don't forget to stamp the tickets as soon as you get on in the yellow machine at the back of the bus. I found the metro to be the best option to the Vatican (as recommended by our hotel).
We didn't use taxis as I have read too many horror stories of overcharging. We flew with Ryanair to Campinio Airport and the Terravision bus only cost ?4 each way.
As you would expect there are loads of restaurants and but I would advise you to perhaps avoid the touristy looking restaurants and go for a little trattoria where the locals eat, you will see them all over the place down little side streets. We asked for recommendations at our hotel, but they sent us to the touristy places(!), which were fine but we found the food to be better and more authentic in the little local places we found ourselves. You will know the tourist versus the local places when you see them. The pizzas and fresh pasta dishes were AMAZING! We all really enjoyed the food (yum, yum).
Our highlights included:
The Colossium - of course. We got a group guided tour, it only cost 4 euro extra (on top of the cost of the ticket and well worth it). We spent hours here, our kids loved it. Watch Gladiator before you go to get you in the mood. We went to the Forum across the road afterwards, not as interesting for the kids, so we didn't spend too long here.
Climbing the dome at St. Peter's - spectacular view. The canopy over the alter was made by Bernini from bronze used from the Paneheon.
Victor Emanuelle Mounment - we took the lift to the top, good views too. When you come down the lift and are walking away from it there is a church on the left hand side, worth a visit, really beautiful church.
Julius Ceaser's Forum. You will see this from the top of the Victor Emanuelle - it is located on the Colissium side of the view, on the left hand side. If you look directly down you will see a site with 3 columns (i.e. directly by the main road). You cannot gain access to Ceaser's Forum, but when you leave Victor Emanuelle you can walk around the corner for a close-up view. Ceaser built a lavish temple to Cleopatra (following their affair) and these columns are all that remain of the temple - I just found that so fasinatating. Everything that they have excavated is laid out for you to view, truely incredible (btw Julius Ceaser and Cleopatra had a child, I never knew that!).
We didn't get time to see the Capital Museum, but I believe it is well worth a visit. The Vatican Museum was good, but a bit long with kids, unless you are really into art everyone just wants to get to the Sistine Chapel. The Sistine Chapel is amazing (of course) but there are also beautiful gold leafed ceilings all the way through the Vatican Museum, which I thought were just as beautiful (shows what I know lol).
You have to see the Trevi fountain - the streets around this area are cobbled and full of little shops but sadly we didn't have time to explore them.
The Panetheon is another must see.
The Spanish steps are nice, but if you are stuck for time I don't think they are worth making a detour for (they are only steps with an o.k. Bernini fountain at the bottom). There is another lovely view from top of the steps (take a left and walk in the direction of Villa Medici, but it was raining the day we were there so we couldn't see much). The shops around here are mostly designer, so not much to buy really.
I would highly recommend Rick Steeves books on Rome, excellent advice and recommendations (he also recommends plenty of restaurants). We had our 3 children with us so we didn't eat anywhere really special or expensive.
The only downside to Rome is the traffic. Trying to cross the road was a nightmare, especially at the huge intersections around the main sights. The cars fly around you on the pedestrian crossings, you are supposed to walk onto the crossing with confidence (!) but if you are nervous the cars will come at you even more, it was a nightmare with 3 kids tbh. In the end we waited until we saw Italians crossing and we jumped behind them and cross with them.
We have 4 nights and 5 full days in Rome and just about saw what we wanted. There is sooo much to see - we fell into bed exhausted every night.
The weather was mixed when we were there. We had some rain and when it rained it soaked you, so be warned. We also brought hats/gloves/scarfs too, and we did use them early in the morning and in the evening when the sun went down.
If you have any other questions, just let me know. You will have a fantastic time.