"I love you to the moon and back" is more of a popular phrase than it is a poem. Many poems have been written with the title, but there is not one particular one that stands out as the most popular.
Some of the authors that have written an "I Love You to the Moon and Back" poem include Tina Foley, Trevor, Mibba and James Carter. The origins for this saying and these poems are not completely clear, but they possibly stemmed from the book "Guess How Much I Love You" written by Sam McBratney. The book states many different scenarios for how much the parent loves the child, and one of the scenarios is that the parent loves the child to the moon and back.
The way it stands out as a phrase has made it extremely relevant in popular culture. It is something that quickly rose to popularity on social media networks and has continued to remain a big phrase. "I love you to the moon and back" is a popular thing that parents say to their children or other loved ones when they want to express love for them; it can be used interchangeably with "I love you more than all of the stars in the sky" or "I love you more than you could ever even imagine."