Authorities detained Daniele Bosio Saturday after being tipped off by a child welfare group that he was seen alone at a popular resort in Laguna, just south of Manila, with three boys from the capital.
The boys were aged 9, 10 and 12, police said.
Officials from the Italian Embassy in Manila have visited Bosio in detention, said Chief Superintendent Jesus Gatchalian, a regional police director.
"Bosio is a diplomat but he is not assigned here in Manila, so we are wondering what he is doing here," he said.
Gatchalian said investigators were still checking when Bosio, who is assigned to Italy's embassy in Turkmenistan, arrived in the Philippines and how he got to meet the boys.
There was no statement from the Italian authorities.