It’s not unusual for the walls of a kindergarten classroom to be plastered with colorful posters.

But a poster in a Somerville, Mass., school caught the attention of Georgy Cohen and her husband, Rick Healey — and it didn’t have anything to do with ABCs or washing your hands.

Handwritten in multicolored markers, the neat block print read:

Lockdown, Lockdown, Lock the door

Shut the lights off, Say no more

Go behind the desk and hide

Wait until it’s safe inside

Lockdown, Lockdown it’s all done

Now it’s time to have some fun!

Accompanying the text were three images: a lock with a key in it, a hand turning off the lights and a person holding a finger to his lips. The words, meant to be sung, are set to the tune of “Twinkle, Twinkle, Little Star.”

Healey told The Washington Post that he and his wife came across the poster while they were visiting the school last week as part of an official tour for parents who plan to send their children to kindergarten in the fall. The couple have a 5-year-old daughter.

He said he was “saddened” to see the poster, but recognizes why the approach may be necessary in an era of school shootings.

“I can understand why it was put to that song, to help kids understand it without panicking,” he said. “ It’s something a 5-year-old can wrap their brain around without having the full meaning behind it apparent to them.”

He declined to identify the school, but several news outlets reported that poster was at Somerville’s Arthur D. Healey School — no relation to Rick Healey.

In a joint statement, Somerville Mayor Joseph Curtatone and Public Schools Superintendent Mary Skipper said the poem was an example of a teacher’s strategy to “help her young students stay calm and remember the key steps they would need to follow during a drill or real emergency,” HuffPost reported.

“As much as we would prefer that school lockdowns not be a part of the educational experience, unfortunately this is the world we live in,” the statement said.

The “Lockdown” poster in Somerville has drawn mixed reactions.

Cohen tweeted a photo of the poster, adding the message: “This should not be hanging in my soon-to-be-kindergartner’s classroom.”

But later she tweeted a message saying that the school was “doing exactly what they need to be doing.”

She urged her followers to talk to legislators about the importance of gun reform.