EAST COMPTON (CBSLA.com) — Authorities say a boy was taken to a hospital Monday in “extremely critical condition” with internal injuries and a man has been arrested.

The Los Angeles County Sheriff’s Department described the child as a 13-month-old boy, and investigators suspect the child was beaten in East Compton.

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Investigators said the mother’s boyfriend was taken into custody after someone called Sunday about a baby not breathing.

“He admitted to hitting the child either earlier in the day or the night prior,” Lt. Steve Jauch of the LASD said.

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The baby’s grandfather told CBS2’s Erica Nochlin the family was celebrating another child’s birthday Saturday night, but doesn’t know when the alleged beating happened.

“I think it’s critical for us to talk to the mother. Talk to the other children. Talk to friends. Family. We’d be obviously interested in finding out if this is an isolated incident or if this is something that’s been ongoing whether towards our 13-month-old or the other children in the home,” the lieutenant said.

Lt. Jauch said the three other children, who live in the home, are with other relatives.

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Bail for the suspect, who remained behind bars, has been set at $100,000.