The incident involved a eucalyptus tree at Linda Vista Children's Center in the 1200 block of Linda Vista Avenue.
The children were outside for lunch in a play area adjacent to the children's center when the tree came down. A large limb, more than 20 feet in length, trapped the 2-year-old girl, according to fire officials.
First responders arrived quickly and the little girl was transported to an area hospital in critical condition. Two other children were also transported with minor injuries, fire officials said.
The other injured students were 3 and 4 years old.
According to officials, the critically injured girl is beginning to show some signs of improvement after the accident.