Our family (two adults, two kids (11 and 9 years old) had a very good experience renting bikes from Fuori di Ruota for a few hours and biking the Park of the Aqueducts. They were very friendly and provided a map of the park. The bikes were a bit old but totally fine for what we were looking for and the rental was reasonably priced.
This was a fantastic part of our 5-day visit to Rome. We took the subway to a nearby stop, walked to Fuori di Ruota, rented bikes for 2 hours, road around the park (which is just across the street from the shop) and then had a delicious late lunch at a local restaurant before heading back to the heart of the city.
The park is ideal for a casual ride around. It is flat with a good number of interconnecting dirt trails that are in fine condition. It is also beautiful and you get to ride next to ancient aqueducts and explore them a bit.
Just a note that this is a small bike shop. I would definitely contact them in advance of going out to rent from them to make sure they will be there and haven't rented all their bikes. As I mentioned, the bikes we rented were absolutely fine but a bit old; it was a bit hard for me to understand but I believe they said they had already rented their newer inventory. To that point, they don't speak English. If you don't speak Italian, I would recommend emailing them to make the communication easier. I emailed the morning of our rental and got a prompt response.
Bottom line, this bike shop enabled my family to have a wonderful experience exploring a unique part of Rome. I would 100% recommend doing this on your trip.