A 6-month-old boy was in critical condition Monday night after a white pickup truck struck him, his mother and another boy, 3, as they crossed Kalanianaole Highway in Waimanalo.

They were in a crosswalk at Oluolu Street, police said.

The female driver fled the scene, leaving the truck behind, and police arrested a 38-year-old man for allegedly hindering prosecution, police said.

Emergency Medical Services said both children were treated for head injuries. Paramedics transported to the hospital the 6-month-old baby in critical condition and the 3-year-old in serious condition.

Police dispatch said the accident was reported at 6:46 p.m. from the 7-Eleven near Waimanalo Beach Park.

Police Lt. Carlene Lau said the woman was also injured, but was in good condition.

The highway was closed near Puuone Street. Traffic was rerouted to allow police to conduct an investigation.

A baby stroller remained partially under the front of the truck while police investigated. The truck, headed east, didn’t come to a stop for 60 feet.

Police are looking for a woman they believe is in her 30s, whose name is Annie Akau. She is 5 feet tall, weighs 144 pounds, has brown hair and brown eyes, wearing a gray T-shirt, shorts, slippers and was last seen with an infant.

“I heard the screeching tires,” said Lynn Mattson, 64, who lives behind the 7-Eleven. The baby, she said, “was still stuck in the stroller in front of the truck. … The 3-year-old was lying on the corner in front of the crosswalk.”

Mattson said the family just had dinner at the father’s mother’s home. The mother was pushing the stroller with the baby and the father was walking right behind them.

When Mattson arrived, the father was yelling and the mother was screaming, Mattson said.

She accompanied the father and got the baby out of the stroller. Mattson held the baby because the father was so distraught.

“He was just a little thing,” she said. “All he was doing was gasping and vomiting.”

Mattson said the baby and his mother went to Castle Medical Center and that the 3-year-old was taken to the Queen’s Medical Center.