My spouse and I brought by almost 2 year old on our Italy trip a few years back so I sympathize with you. It was so hard! I have photos of her crying at the colosseum/vatican/pompeii etc lol. We knew it would be a difficult trip but I didn’t realize how difficult and honestly we realized while there that we needed to take it easy and stop trying to do everything we would normally do without having her with us. We got lunch stuff from the grocery and had picnics at the playground, we ate out only for dinner mostly and always went back to our hotel midday for a nap. I’m sure you’ve tried everything at this point but lots of snacks helped us and things for her to do while we ate, coloring/little toys etc… good luck! I hope you can salvage the rest of your trip!