Looking chic in a red, black and white checked jacket, the elegant Princess paired it with a black turtleneck and wide legged trousers.
Carrying a large bunch of flowers Mary received an adorable reaction from the children at the event as they peered out of the window and smiled at the princess.
The Children's Day was held for the first time on the anniversary of the United Nations Children's Convention
Now the day has become a tradition, and this year is the topic "Children in World Destinations".
Mary, originally from Tasmania, stepped out without her husband, Crown Prince Frederik.
The couple met when Frederik visited Sydney for the 2000 Olympics and didn’t even know her future husband was royalty at the time.
“The first time we met we shook hands,” she told AWW. “I didn’t know he was the prince of Denmark. Half an hour later someone came up to me and said, ‘Do you know who these people are?’
The couple were engaged in 2004 and now have four children.