Katie Rich, a writer for “Saturday Night Live,” has been suspended from her position at that show following a widely criticized post she made Friday on her personal Twitter account in which she mocked Barron Trump, the 10-year-old son of President Donald J. Trump.

She was suspended immediately after her tweet, and her suspension is indefinite, according to someone familiar with the plans at “S.N.L.,” who was not authorized by NBC to comment on personnel matters.

That tweet on Friday, during Mr. Trump’s inauguration ceremony, drew widespread condemnation, and Ms. Rich subsequently deleted the post (which said “Barron will be this country’s first homeschool shooter”) and deactivated her Twitter account. Her name did not appear in the closing credits of “Saturday Night Live” in its broadcast on Saturday.

On Monday afternoon, Ms. Rich reactivated her account and posted a message that said: “I sincerely apologize for the insensitive tweet. I deeply regret my actions & offensive words. It was inexcusable & I’m so sorry.”