The near drowning happened at a home in the 12000 block of Susan Drive in Knollwood.
The children, who are believed to be 2 or 3 years old and two of three triplets, were rushed to Providence Holy Cross Medical Center in Mission Hills. Officials said one was alert. The condition of the other was not known.
The circumstances of what happened are still unclear, but police said adults were home at the time.
The Los Angeles Police Department's child abuse unit was investigating to see if foul play may have been involved.
It was incorrectly reported earlier that the victims are twins. They are two of three triplets.