Watch Secret Life of 4, 5, 6 Year Olds UK

Having kept the Girls and Boys apart last week now it's party time. Five of the Girls and five of the Boys are returning to discover they have to share the play centre with the opposite sex - how will they react? And will our experiment bear out research suggesting that at 5 years old Girls and Boys positively benefit from mixed gender groups.

This time, as a new intake of fascinating five year olds arrive for work and play, we explore the difference between boys and girls, seeing how they interact with each other and how their sense of gender roles is ingrained at such a young age and whether there is a marked difference in behaviour.

In the final episode of the series, the five-year-olds return but are joined by some new faces. Competition is something we often want to shield children from but it's an integral part of every five-year-olds life. How will they cope with winning and losing when challenged to compete against each other.

This week sees ten new five-year-olds arrive at the play centre. With a year of school under their belts, these children are asserting their independence and becoming more and more interested in exploring the adult world around them. How will they cope when they encounter other children who are different to themselves?

The week starts off with a bang as new girl Milana clashes with last week's alpha girl Evie-Rae. Tensions continue to rise and sparks start to fly as the girls are teamed together for a building task. Milana's play style threatens to alienate her completely from the group, until she hatches a cunning plan to turn it all around.

In this first episode, it's the four year-olds. We observe as a new group of 4 year olds take their first steps towards independence, forge friendships and find their own feet away from the family. And sharing the classroom, in an incubator, 10 chicken's eggs are about to hatch...