So if I buy the Roma Pass what do I have to do to get in the Coliseum?
From the FAQ page of the Roma Pass website; I suggest spending some time with this page as it answers a lot of questions:
http://www.romapass.it/en/FAQ/
For the Coliseum, Roma Pass holders can make a reservation in three ways:
On-line, on the website ecm.coopculture.it – required booking fee 2€ (with credit card)
Call center at 0639967575 – required booking fee 2€ (with credit card)
At the Roman Forum - Palatine ticket offices, only on the day of the visit (upon availability)- the ticket office will issue a free receipt with the admission time. MY NOTE: the time slot assigned may not be optimal. It's possible they may also not have open slots at all that will work your particular visit.
Free booking can be made only on the day of the visit at the Roman Forum - Palatine ticket offices (upon availability); the ticket office will issue a free receipt with the admission time, for that day.
Roma Pass holders can make a reservation online or by calling on the day of the visit. The booking fee is required.
The online booking or by call center will issue a note with PNR which will be changed for a receipt with an admission time at a reserved counter at the Roman Forum ticket offices. This receipt is not valid for entry, but only for the time slot.
Roma Pass holders, through the security checks must go to the access gate of the Coliseum, presenting their Roma Pass, otherwise it’s not possible to enter even if they have an time booking. Afterwards, Roma Pass holders will enter the Coliseum through a dedicated gate controlled by Coopculture’s staff.
Roma Pass is valid only for ordinary access to the monument (Arena, Sotterranei and Belvedere not included)
Visitors with free admission who enter with Roma Pass holders already booked an admission time, can collect the free ticket at the ticket office skipping the queue. The booking fee is € 2.00.
Is it correct that teenagers from the US are free at these sites
(Coliseum, Forum and Palatine Hill)?
Yes, If under 18: bring their passports for proof of age. They will pass the security entry with you - if you are using pre-purchased tickets or a pass - and you will then pick up their free tickets at the ticket desk. If using the Roma Pass, see the last line of the text paragraph above. However, they are not free on city transport so if you intended to use Roma Passes for that, you'd have to purchase separate tickets or 1 -day/multi-day transport passes for the teens. Guided tours of the 3 sites are also not free for teens.