Ranging from an 8ft dinosaur to a three-eyed girl with a pet cloud, the children were able to finally meet the characters they'd created in their head.
Rankin then photographed the children with their models to create a striking photo series.
"Chloe": made by BlinkInk for Mable Brim
Arvid Harnqvist and Amar Marwaha, the creative team who initially came up with the idea, said they wanted the project to immortalise the imaginary friends in children's heads.
"Children create many amazing things - take their imaginary friends for instance," the pair said.
"They are talked about all the time and often become part of the family.
"But when the child gets older, these marvellous creations fade away."
The project began in September, when more than 60 children were invited to a workshop and asked to draw their imaginary friends.
The characters were brought to life by Tsuneo Goda, the creator of the Japanese cartoon icon Domo Kun; Aardman, famous for their creation of Wallace and Gromit, and Becky & Joe the two creators of the video series 'Don’t Hug Me I Am Scared'.
Rhian Harris, director at V&A Museum of Childhood, said about the campaign "has brought together children’s imaginations with some of the UK’s most exciting designers and artists, in an exciting project to bring their 'imaginary friends' to life for all to see.
A creative at Aardman, who made 'Monster' for a boy named Leo, said the team loved joining in with the project, commenting: "An imaginary friend with three eyes, four arms and four legs.
"What’s not to love! We’ll play that game any day."
View the six drawings and real-life models of these children's imaginary friends in the slideshow below.
Watch the video above shows the children's reactions upon first seeing their their imaginations brought to life for the first time.