Moey Yin, a teacher, was driving home from school when she noticed a frog in her car on Friday, police said.
She panicked and lost control of the vehicle, which rammed into a tree near the pond.
Moey died on the spot while her son, aged 8, and daughter, 9, sustained serious injuries.
The son suffered a broken leg while the daughter was still unconscious and had been warded at the hospital's Intensive Care Unit.
The incident is being investigated.
