Suddenly Millie had moved in: three-year-old Paul planned to go to the cinema with her, they cooked together in the children's kitchen and drove through the apartment together in the bobby car.
But Millie wasn't always there, she came and went as Paul liked or suited his routine: if he were to clean his room, he refused, arguing that Millie had made the mess and therefore had to clean it up.
The problem was, Millie was invisible to everyone else.
The fact that Paul's parents found out about their new playmate is not everyday, because children usually keep their imaginary friends to themselves, reports Renate Schepker, professor on the board of the German Society for Child and Adolescent Psychiatry, Psychosomatic Medicine and Psychotherapy.
Only when there is a lot of trust do children also talk about their invisible comrades.
The boyfriend or girlfriend can be very different in gender and age.
A mother tells that her daughter had two older men as imaginary friends who also sat at the table during meals and for whom the table always had to be laid.
Another child had a friend in England who kept coming up with spectacular things: sometimes she was in the hospital because of an accident, sometimes she flew to America, sometimes her parents had died.
According to Schepker, the fantasy friends are a way for children to sort out reality.
Similar to Santa Claus, children create spaces with these figures to interpret the world differently than adults.
The friend helps to regulate the feelings
The everyday problems that a small child deals with are often banal from an adult's point of view: it falls or is annoyed that it cannot climb like the big children on the playground.
For a child this is existential - and this is exactly where the imaginary friend can help regulate emotions.
An invisible friend is not a conscious decision, but an unconscious process, like playing itself, says Schepker.
The child also becomes capable of this form of expression.
The phenomenon is most common in children around the age of two.
But what does the child need cognitively to invent invisible friends?
"This includes imagination, the ability to symbolize and language," says Norbert Neuß, Professor of Childhood Education at the Justus Liebig University in Giessen, who has done a lot of research on imaginary friends.
The phenomenon is comparable to diary writing in adults.
The child invents the friend to enter into dialogue and reflection on the world.
The psychosocial development of the child is supported in dialogue.
"An invisible friend," explains Neuss, "always has a positive function: He is a companion, encourager, comforter, suggestion box or playmate.
It supports as an emotional railing in a world that is characterized by irritation.”
Parents' fears as a reason
A trigger could be, for example, a sibling that is suddenly put in front of you.
In such situations, the emotional balance in the family needs to be renegotiated, with the invisible friend helping to bring the emotional imbalance back into balance.
Separations, divorces, relocations, or the death of a family member may also involve invisible friends.
But the parents' fears could also be a reason for the fantasy figure.
Neuss reports on the example of a boy who had an invisible friend.
This had no name, but was called "the friend who goes to the ceiling".
The child liked to climb trees, but the mother was very anxious and repeatedly forbade the boy from climbing trees, which hindered his development and the need for exercise and testing limits.
For this reason, the invisible friend appeared, so that the child could say to his mother: "You don't have to worry, my big friend is with me and takes care of me."
This friend, explains Neuss, gives the child the opportunity to experience things that its mother is afraid of: "In this case, it has a stabilizing function." One should not imagine the invisible friend as split off from the child would be - "but he is a part of being", he belongs to the identity of the child.
"It sort of springs from their creativity." That's why parents shouldn't speak negatively about the invisible friend either, as this is a direct insult to the child.