Activity: The Vatican. Metro Stop: Ottaviano and then walk 10 minutes south on Via Ottaviano. Cost: €15 (reserve online!) Hours: 9-6.
Get to the Vatican at least a half hour before your reservation time. Be forewarned that this museum is hot (no AC), smelly, crowded, and massive. If your kid is slow, a stroller is a must. Many hustle past all the other art to get to the Sistine Chapel. Nobody will judge you if that is what you choose to do. You walk through the whole darn thing to get to the Sistine Chapel and there are no shortcuts. Let me know if there is still a guy who repeats "NO PHOTO" over a loudspeaker again and again in the Sistine Chapel.
The eateries around here are overpriced and cater to tourists (not a lot of good local food). So I am going to send you on a bit of a walk to a local pizza place called Ristorante La Rustichella outside of the Vatican walls.
Rustichella: Via Angelo Emo 1
Whew, that was exhausting but you did it! Go back to your hotel and take a siesta. I personally did not enjoy Vatican City. It's just too much for me. So if you want to skip it and have a free afternoon, I am sure you will be back in Rome one day to see the Sistine Chapel and The Vatican.