Day pack recommendations

I can’t fully answer your question since I’ve never traveled to Europe with young ones. But I did want to say you should be very cautious about putting valuables like your wallet in a backpack. It’s just too risky. A backpack is great for water bottles, sweaters and tissues. But keep your money, cards and passport in a more secure location, like a neck wallet or a money belt.

Honestly, I’d just stay minimalist and go with your crossbody bag. IMO, you’re already doing it the right way and it’ll feel more natural.

You’re gonna be in a modern town that sells stuff you may need. I think you can get creative about parsing snacks and supplies for a single outing. e.g You don’t need a full box of wipes every day, so use a ziplock with a days supply.

Take it from a parent who used to treat every outing like I was on an expedition to some wasteland

We're way past the traveling-with-young-ones stage of our lives, but we travel with a crossbody bag to hold wallet, phone, phone charger, other small stuff but large enough to hold a light sweater for me; I will put a small water bottle in it as well. We also bring with us on our trips a string bag or similar, I now have an ultra-light-weight bag that can go over my shoulder. We use that for anything else, such as another layer of clothes, umbrella, guidebook, etc. Also good for trips to the store and picnic lunch items. This bag is good for anything that we don't need to worry too much about, in terms of being stolen.

I am not sure where you are headed but I would check this website or even reach out to her directly.
She seems to have a lot of tips, at least for traveling in Italy.
https://mamalovesitaly.com/category/italy-with-kids/

I really like Aer, all their products have great zippers, durable materials, and overall smart design. I always bring my Aer Day Sling 2 on a trip to Europe, probably a bit smaller than what you're describing but they have a full line of bags.

Thank you everyone for all the replies and suggestions! I'll definitely look into specific bag suggestions and also your packing method!

@ Chris - yes, I am the same. I need a constant reminder that stores are available and I can figure it out, ha! I'm better at home about it because we just keep our stuff in the car and we're never far from it since there's literally 0 walkability or public transport where I'm at.

@alcaraz.ann - I saw her website and have been looking there. Very helpful in relation to car seat info also!

hmm .... I typed a response here last night but don't see it now. :-(

I like security bags. I've only used PacSafe but there's at least TravelOn.

I've owned three PacSafes - all for different reasons. If you can define what you need to carry you'll have defined what pack you're looking for. My first PacSafe was great for airplane travel as the "personal item" and for getting to the lodging but was/is too large for use during most days.
I made this video, 6 years ago, to talk about features but mainly to think through "will it carry what I want to carry"
https://www.youtube.com/watch?v=6GB7kgmecNY