It's a Secret Tweenies : Season 2 Episode 27

Milo will not reveal what is inside his box, claiming that it is a secret – much to the other Tweenies' annoyance. They are cross and say that friends should share their secrets. They make their own boxes and tease Milo by refusing to say what's inside them. Eventually Milo opens his box and reveals his secret, but can he persuade the others to tell?