Alesia Thomas died at a hospital after the confrontation July 22, the Los Angeles Times reported.
Officers arrived at Thomas' South Los Angeles home to investigate why she surrendered custody of her children, ages 3 and 12, to police earlier that day. She had said she was a drug addict and could not take care of the children, the Times reported.
Thomas resisted arrest for child endangerment and one officer knocked her to the ground by sweeping her legs out from under her, the police account of the incident said.
A patrol car's video camera captured the altercation, in which a police officer kicked Thomas in the genitals. The officers' accounts made no mention of the kick to her body.
Thomas was eventually put into the back of a patrol car and can be seen on the video breathing shallowly and then apparently not at all.
"I take all in-custody death investigations very seriously," LAPD Chief Charlie Beck said in a statement late Thursday. "I am confident we will get to the truth no matter where that leads us."
Four officers and a sergeant were removed from field duties as part of the investigation, the Times reported.