Police say the two sisters, ages 10 and 12, happened upon the man near the Greenbelt and East 48th Street around 2 p.m.
Officers say the girls told them that the man pulled the knife and began wielding it at them in an agitated state, so they ran away and called police.
Police say when they arrived on scene, they found Tommie Salmon occupying a makeshift campsite in the area. After questioning him, officers say he offered incriminating statements about the incident and he was placed into custody.
Garden City Police say Salmon has been arrested and charged with two counts of aggravated assault with a deadly weapon.
Neither of the two girls were hurt and police say they did the right thing by removing themselves from the area and calling for adults and authorities.