You might not think tiny children have much of a secret life - but it turns out they do, and it makes for gripping television.
The award winning series is billed by Channel 4 as offering an 'intimate and fascinating window on the ups, downs, tears, tantrums and triumphs that unfold when a class of children meet each other for the first time'.
It's back for a new series - and producers are looking for children and parents to take part.
According to the application form the children will be observed throughout by leading scientists and psychologists, who will give insights into child development.
Filming will take place between Monday July 30 and Friday August 24.
Parents are asked to describe their child's character, interests, what they like and dislike about school or nursery and whether they use technology, as well as information on disabilities, medication and allergies.
Parents must upload a video clip of their child to help the selection process.
A spokesperson said: "We are currently looking for 4 and 5 year old children and their parents to take part. Your child would be needed for a week or two of filming during the summer holidays."