Entrance to museums for minors

It may be different at other places but when I bought tickets online to see the Last Supper using Viva Ticket, I entered the number of people in my party and there was a spot to enter whether I wanted adult or free (under 18 tickets). At that time both my children were under 18 so I was charged 11€ for 3 admission slots. That was in 2015, but I think it is still the same. Just thinking about it logically, the tourist authorities must know that they need a way to count children for the purposes of tracking the number of people allowed in if they are limiting entry.
Edit: Just remembered that it is the way I described at the Last Supper at the Accademia in Florence as well: you order the number of full price and free tickets that you need.

Anyone under 18 gets free admission to state run sites. Private sites charge what they wish to charge. Most will have a category for "free tickets/tours". You just enter the number needed.

Be sure to bring passports for proof of age for the free tickets.

Donna

Private sites charge what they wish to charge.

True. For instance, there's an entry fee at the Vatican Museums for children between ages 6 and 18. The state museums which allow free entry for under 18's may also require you to make reservations for them or pick up their free tickets onsite so referencing individual websites for the attractions is advised.

At state run sites you'll always need to pick up free tickets at the ticket booth so they can see you meet the age requirements. Most private sites have the same rules about picking up free or reduced priced tickets. Usually only full priced tickets can be printed at home because everyone can buy those.

Donna