In Massachusetts, a class of five-year-olds are learning this rhyme - set to the lullaby "Twinkle, Twinkle, Little Star" - so they know what to do during a school shooting.
Cohen said he isn't upset with the classroom teacher for hanging up the poem.
"That's to the tune of the alphabet song, and Twinkle Twinkle... what a horrifying contribution to the songbook", said Margot Bloomstein on Twitter about the lockdown song being implemented in the kindergartners' classroom. The photo has been retweeted more than 14,000 times.
In a follow-up message, Cohen said her child "was excited about [a drill] as a game to see if you can stay quiet for "one whole minute".
Healey told The Washington Post that he and his wife came across the poster while they were visiting the school Wednesday as part of an official tour for parents who plan to send their children to kindergarten in the fall.
One US kindergarten has posted a nursery rhyme teaching kids to hide during a school shooting.
"It's jarring", Cohen told the Globe in a telephone interview [on 7 June 2018].
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"These are the things they unfortunately have to do", she said. She found a nursery rhyme taped to the blackboard that presented the basic instructions of what the children need to do in an active shooter situation in a cutesy, nursery rhyme-style song.
A mom expressed mixed feelings about her daughter being prepared "if a bad guy comes to school".
In a statement, Superintendent Mary Skipper and city Mayor Joseph Curtatone praised the teacher's creativity, but said they regretted how common lockdown drills had become.
"To be shocked by it is important", she added.
Following the overwhelming response to the tweet, Ms Cohen requested that people call their congressional representatives to advocate for gun reform or support organisations like gun safety advocacy group Everytown and Sandy Hook Promise.
There have been 23 shootings in USA schools this year alone which have resulted in one or more deaths.