"Lockdown, lockdown, lock the door. Shut the lights off, say no more."
Sung to the tune of popular nursery rhyme Twinkle Twinkle Little Star, the lyrics on a poster put up in a Massachusetts classroom will give any parent the chills.
"This should not be hanging in my soon-to-be-kindergartener's classroom," Georgy Cohen wrote on Twitter on Wednesday (June 6).
She was touring the school her five-year-old daughter would be attending this fall when she spotted the ominous sign.
At her pre-kindergartener programme, the girl was practising active shooter drills and was "excited about it as a game to see if you can stay quiet for one whole minute," Cohen tweeted.
With a spate of school shootings this year, teachers, students and parents alike have expressed fear and worry over safety issues in the institutions.
Many of them lobbied for gun reform after 17 students in Parkland high school were killed by an ex-student with an assault rifle this February.
A measure recently introduced to protect school children in the event of a shooting include bulletproof shields.
Meanwhile, president Donald Trump showed support for arming "adept" teachers to prevent or shorten school shootings.