Basically every single church in Italy will have both paintings as well as frescoes, all with various stories from the Bible, from the apostles to saints, from Mary and baby Jesus to the Last Suppers. Old Testament as well as the New.
Many often depend on whether a church is dedicated to a saint or to a patron saint, the art frescoes cycles might be quite dependent on who ordered the commission and who they wanted to honor.
Take, for example, Santa Maria Novella Church - you have the "Trinity" by Masaccio as soon as you enter by the side door and soon after the Crucifix made in wood hanging in the center of the church. Behind the main altar, the Tornabuoni Chapel by Ghirlandaio and his workshop depict stories of both the Virgin Mary (on the left side) and to St. John the Baptist (scenes on the right side) while the Strozzi Chapel to the right of the Tornabuoni chapel is dedicated to St. John the Evangelist. So every single part has stories dedicated to someone, you could choose to visit Santa Maria Novella and dedicate time to just one church. This is not even half of what you can see inside, here are more details:
Visit the Santa Maria Novella Church just a short walk from the Florence train station and admire its majestic Gothic beauty. One of the more important & beautiful churches in Florence
www.visitflorence.com
The Spanish chapel and the cloisters are all frescoed - to be honest, I have most appreciated this entire church when I went with a guide that explained a lot of the art inside.
Santa Croce is very similar, it has many chapels with frescoes including Giotto in two of them, with fresco cycles dedicated to the life of St. Francis of Assisi and to St. John the Evangelist, while the one behind the main altar is by Gaddi dedicated to the Holy Cross (as the church is dedicated to it). Here are more details on Santa Croce -
https://www.visitflorence.com/florence-churches/santa-croce.html
The Uffizi and Accademia galleries are shock full of art that was originally inside churches and which is generally 100% religious in terms of subject matter - take a look at this guided tour for example -
https://selector.viator.com/tours/F...rence-with-Child-friendly-guide/d519-107245P6
There are others like it, but what I would suggest is that you think of a theme you'd like the kids to use and THEN use that as a sort of unifying theme for a sort of scavenger hunt: for example, the virgin Mary with baby Jesus --- every time you go someplace, have the kids find the paintings that have Mary with baby Jesus and find them across all the sights. Make a list and discuss what was different.
Another great one in Florence are the Last Suppers - get to know the story beforehand, then go visit all of them - there are 8 stops at least:
https://www.visitflorence.com/what-to-see-in-florence/last-suppers-in-florence.html Oh I just saw I need to update the Santa Croce one, as the same hall that has Taddeo Gaddi's fresco also now hosts Vasari's Last Supper, a painting.
Let me know if you have any specific questions with the info I have and any other questions I can help you with!
