GREAT FALLS (AP) -- The 2-year-old boy whose body was found last week in the trunk of his mother's vehicle was a happy child who loved toy cars and was nicknamed ''Hymmie,'' family members said.

Family gathered in Browning to remember James Many White Horses II on Saturday, a day after authorities discovered his body and arrested his mother, 31-year-old Summer Many White Horses, on allegations of killing him.

''He was just an active little boy. Just a happy, bubbly-eyed little kid,'' said Elissie Buffalo, Summer Many White Horses' aunt. ''He was loved dearly.''

Marie Franks, Summer Many White Horses' grandmother, added that relatives were ''shocked and hurt'' by his death.

James was last seen with Summer Many White Horses on July 21, according to a missing persons alert issued by the Montana Department of Justice.

That night, a Great Falls police officer spotted Many White Horses' speeding car and followed it. Many White Horses ignored the officer's lights and siren, drove through several stops signs and crashed into a parked truck, said Cascade County Attorney Brant Light.

She failed a breath test and was arrested on several misdemeanor offenses, including driving under the influence, Light said. Many White Horses was taken to jail, and her car was towed to a repair shop.

Police saw no reason to search the vehicle, Light said.

On Friday, Many White Horses told police that her son had been in the trunk of the car since the night of the crash, Light said. Police found the boy's badly decomposed body Friday afternoon.

Summer Many White Horses was arrested a short time later on suspicion of deliberate homicide, tampering with evidence and obstructing a peace officer. She is expected to be formally charged today in district court.

On Saturday, Light revealed that Many White Horses also has an 11-year-old daughter, who was in the back seat of her car during the July 21 crash. The girl was placed with the Department of Health and Human Services when Many White Horses was arrested.

Many White Horses was released from jail Aug. 10.

Authorities didn't know she had a son until the state gained temporary custody of her daughter around Aug. 14, Light said. Police then questioned Many White Horses, who gave them no indication of the boy's whereabouts.

Authorities thought Many White Horses may have taken him to Oregon or Washington. Light said the boy's father lives out of state.

A missing-person advisory was issued Thursday. Police found Many White Horses in Great Falls on Friday and questioned her again; she eventually told them where the boy was, Light said.

''There's so much we don't know yet,'' he said. ''None of us had any idea he would be found in a trunk. We're stunned, obviously.''

Many White Horses told family members her son was being taken care of in Great Falls, which didn't alarm them because she has a brother there and it was not unusual for relatives to look after her children, Buffalo said.

Many White Horses gave birth to James in a Billings prison, and an aunt raised him for more than a year before a judge returned him to his mother after her release.

Buffalo said it was painful to let the children live with their mother, a registered violent offender. Many White Horses' criminal record includes convictions for aggravated assault, felony robbery and resisting arrest, court records said.

''We knew what she was ... a danger. But (the court) thought one way or another she deserved another chance, and we knew she didn't,'' Buffalo said.

James' body has been sent to the state crime lab in Missoula for an autopsy. A memorial service will be held once it is returned to the family.