A Valley Stream man posted child pornography on his Twitter account and was arrested after being reported by the National Center for Missing and Exploited Children, Nassau police said.

Matthew Kerniss, 26, uploaded “numerous images” of child porn in March, April and May, launching a months-long investigation by Nassau detectives in the major case bureau, Suffolk police and the FBI, Nassau police said.

Other details, including why Suffolk police were involved, were not available Thursday night, a police spokesman said.

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Marsha Kerniss, 65, called her son a “good kid” and does not understand why he was charged.

“He’s not like that,” she said. “He wouldn’t hurt anybody.”

She said police and the FBI banged on their front door as the family slept at 6 a.m. Thursday, barging into her bedroom to ask if she had weapons, then seizing her son’s computer and three others.

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Kerniss, of 20 N. Grove St., was arrested and held for arraignment Friday at First District Court in Hempstead on seven counts of promoting the sexual performance of a child and four of possessing a sexual performance of a child.

His mother said he is unemployed because he has anxiety issues and spends much of his time playing video games on his PlayStation when he’s not helping her with chores.

Her son spoke to her briefly Thursday night in a phone call as he was held for arraignment, she said, and he apologized for the morning’s raid. They did not talk about the charges, she said.

“I’m sorry they scared you this morning,” Kerniss said her son told her. “I’m in a lot of trouble. I love you. Don’t be mad at me.”

She said she plans to attend the arraignment, but has felt “sick” over her son’s arrest: “I can’t get my head around this.”