My wife and I are travelling to these two destinations in August (2days rome &1day siena). Whilst we are keen to see plenty of culture our children are only 5+7 years old. any advise on the following;
1.the easiest place to park in siena
2.what is the best time to go to the sistine chapel and are tour guides worth the cost
3.any recommendations for a visit to rome to keep young children interested including ice cream bribes!
4.what to do in rome in the evenings

I was just in Rome for nine days with my daughters, ages 8 and 5. I'll top my trip report for you as it has a list of things to see and do that they enjoyed as well as restaurants and geletarie that they liked. I think a group tour of the Sistine Chapel with a group like Scala Reale is worth the money, however, I don't think young children will get as much out of the experience as you would hope and the Vatican Museums get extremely crowded (especially in August) and it just may be overwhelming to kids. Some people think the best time to go is as early as possible in the morning and some think after lunch is best. I doubt you will find a time where the Sistine is going to be uncrowded. Also, walking the long corridors of that museum can be extremely tiring for children.

Many thanks for your advice. i have since been on the Vatican website but I cant find any clear directions to find the entrance to the sistine chapel-where do we go??? also you suggested a guided tour, can you give us more info on how we might pre book the tour?

We just came back from Rome and our children are 16 and 14. We did St. Peter's and the Vatican on 2 separate days. Some here couldn't understand why, but it just worked out that way, and I am glad it did because the walk to the Vatican/Sistine Chapel from St. Peters is a hike! especially if you have 2 small children. Also, you can wear shorts to the Vatican/Sistine, but not to St. Peters. You can drive up to the Vatican and park right around the corner. The Vatican is around the right of St. Peters. You have to walk a lot through the Vatican to get to the Sistine, but the artwork along the way is beautiful. It was crowded but really not that bad. There is seating all along the perimeter once you get inside the Sistine. Having 2 small children, I wouldn't recommend a tour guide, but that's me. I think they would be bored. You can do it on your own.

Parking for Siena is outside. We did drive into Siena, and parked inside.

The Sistine Chapel is visited as part of the Vatican Museums. You can skip sections of the museum as desired.

Mervyn: Looking at a map of Rome, you will find the entrance to the Vatican Museums/Sistine Chapel on the northern edge of Vatican City, near the intersection of Viale Vaticano and Via Leone IV.
I didn't suggest a tour of the Vatican. I gave you the name of Scala Reale as a tour company that gives tours that are worth the cost which is what you asked for. I don't think children ages 7 and 5 will get a lot out of a tour of the Vatican Museums and Sistine Chapel. If you do want to go ahead with the tour, you can reach Scala Reale at www.scalareale.org.
My daughters have been to Rome twice but I still haven't taken them to the Vatican Museums and Sistine Chapel. I think at this age they would probably hate it and with the crowds in August would definitely hate it. Remember, the museum is not air conditioned and the rooms can get very hot.

IMO, the most convenient place to park in Siena is the huge "Il Campo" parking garage, just inside the city walls on the south side of town, and only a short (5-10 minute) walk from Piazza Il Campo. Look for signs to "Porta Tufi", the nearest gate/portal. You drive about a block past this gate and the parking garage (pay, of course) is on your right.

Another good choice for parking in Siena is inside the soccer stadium near the "Fortezza." Look for signs to the "Stadio" also depicted by a soccer ball. You can park round the clock every day inside the Stadio, but beware of parking around the Fortezza (Fort Belvedere) during the market day, think it's Wednesday. Saw lots of cars being towed away that were parked on the street. If you are in the Stadio on market day, get your car out by 7 AM or you might get stuck. We parked a couple of times for free, I think it depends on the time you enter at night and leave in the morning.