The findings brought the number of rhinos in the Ujung Kulon National Park to from 57 to 60, said Firdaus, a spokesman for the Ministry of Forestry and the Environment.
The three calves - two males and one female - were captured by cameras in April, May and July, said Firdaus, who like many Indonesians goes by one name.
The Javan rhino is probably the rarest large mammal on the planet and they can only be found in the Ujung Kulon National Park, the conservation group WWF said.
But the population has been inching upwards over recent years, raising hopes for the subspecies' survival, the WWF said.