The infant is listed in critical condition at Children's Hospital of Orange County.
The woman and her niece are listed in serious condition at a local hospital. The woman's nephew was not injured.
Investigators took measurements and pictures at the scene, piecing together what happened at the crosswalk
"The investigation is still ongoing," said Lt. Russell Reinhart of the Huntington Beach Police Department. "We're not exactly sure how that happened."
Neighbors said the crosswalk, which does not have a light, gets busy at times.
"It should open up a lot of people's eyes," said Janet Blackstock of Huntington Beach. "I went down there and saw and it was just heartbreaking."
A sign is posted at the crosswalk notifying those who use it that a meeting will be held by the city considering whether it should be removed.
"When we walk to school we use that crosswalk," said Courtney Gillette, who lives nearby. "I think that's awful. There's nowhere for the kids to walk and a lot of kids don't walk with their parents."
But not everyone who lives in the area agrees.
"I would say it's a good idea," Pamela Nava said. "There's a crosswalk up there with a stop light. There's crosswalk down there. I think it was just a shortcut to get into this neighborhood, but there's one shortly down the way where they can actually add a stop light and be able to cross safely."
According to police, the intersection isn't busy enough for a crosswalk.
"There is a safer intersection about 1,300 feet south of that location," Reinhart said. "It's always safer for a pedestrian to cross at a signal than it is at an uncontrolled crosswalk."
Authorities have not yet said if anyone will be charged in the accident.