Tell them not to take too much stuff. The less they have, the easier it is to keep tabs on it and the less there is to steal. Put it all out on the bed then reduce it by half, but don't just take scruffy clothes - for a city you will fit in better with something a little smarter.
When in Rome, which is notorious, I distributed cash and cards over 2-3 tiny purses which I placed in different jeans pockets. Passport I left at my accommodation. Phone in my bra, no handbag. Maybe a couple of tissues and a small tin of hand cream, but for a day trip in a city there really is no need for more than that.
Phones, purses and wallets in front jeans pockets, nothing visible in back pockets. If you need to carry or wear a jacket, only put non-valuables in the pockets. Make sure you don't take cards or phones out where everyone can see you, then away from people. Mend any holes in pockets, and if you can sew, use some spare fabric to add a little depth to pockets to give you more room to stow stuff.
Memorise passwords and phone numbers or at least keep a cryptic note somewhere to help you remember. Keep cards in RFID-secure cases. I use some which are simply like envelopes no bigger than the cards themselves.
There are some really good theft-proof crossbody bags and backpacks availab!e which they might like to invest in, by an Australian company ca!led Pacsafe.
