The Boy with Two Heads COMPLETE mini-series
Basically Chico was the shrunken head of a South American witch Doctor found by the main boy. They became good friends. Chico was magic and called "Chico the Rain Maker" I think to save time and money they hide Chico in a football. So the kid could just carry a football. At one point bullies steal the football and kick it in the Thames not knowing Chico is inside it.