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8 October 2014 Last updated at 08:47 BST
Their parents Lucy and Andy Keher, of Blundellsands in Merseyside, heard giggling after bedtime and filmed them when they found the pair playing the game in their cots.
Mr Keher posted the video on Facebook and it soon went viral, with fans sharing it all over the world.
Twins Molly and Megan Keher have become internet stars after nearly two million people watched a video of them secretly playing peekaboo.