Marco, Tato, Serena, and Leo are nine years old, and they are inseparable friends, ready to defend each other from their schoolmates’ bullying.
All four of them feel neglected by their families: Marco's parents forget his birthday, then pick the wrong cake and present, humiliate him for the unresolved matter of wetting the bed and force him to look after his younger sister. Tato lives with his single mother, who is constantly looking for the love of her life. Serena can't stand her father pressuring her to become the next tennis champion instead of the next champion of snack-eating. And then there's Leo, loved by his grandparents, who give him a brilliant education instead of Leo's parents, who went missing in India.
On the evening of Marco's birthday, all four find themselves together to blow out the candles and unknowingly make the same wish: become adults. In one night's time, they find themselves magically the same age as their parents, but with the same behaviour and thoughts they have as kids.
From now on, funny adventures and unexpected events make them cope with everyday life, such as finding a place to live and a job. Marco will succeed in conquering the woman of his dreams, the irresistible teacher Francesca... But is everything as they had imagined it? Only time can give them the answers they are looking for.