The would-be thief was spotted by a sales assistant, after which the police and deputy manager went through CCTV footage, Milano Today said.
The film showed the boy entering the shop with a 40-year-old couple and their toddler, looking at the phones on display.
The woman approaches the boy when he appears to snatch the phone, but it is left to a sales assistant to stop him stealing it.
He was after the Vertu Ti handset, launched earlier this year for the super-rich, Corriere della Sera reported.
The child left the shop alone, followed a few minutes later by the family who did not speak to staff.
It therefore remains unclear whether the boy was acting alone in the attempted theft.