A man accused of grabbing a toddler by the arm and kissing him twice on the lips at a Sydney aquarium repeatedly apologised when the boy's father intervened and later told police there was a "cultural difference", a court has been told.

Nikhil Bhatia, 28, an Indian national who has been in Australia for just a week, allegedly approached the two-year-old boy who was unrelated to him at the Sea Life Aquarium in Darling Harbour at about 5pm on Sunday.

Sea Life Aquarium at Darling Harbour.

On Monday, Central Local Court was told the toddler was with both of his parents when Mr Bhatia touched him on the head from behind, then moved in front of him and lowered himself down.

A police prosecutor, Sergeant McKinnon, told the court Mr Bhatia grabbed the boy's arm and moved the child closer to him, before kissing the toddler twice on the lips. The boy's father, who intervened, later told police Mr Bhatia used force to bring the child towards him.