The Adventure Series by Enid Blyton

The Adventure Series features Jack, Philip, Dinah, and Lucy-Ann, a group of children who, together with their pet Kiki the parrot, get snarled up in the most amazing adventures you can imagine. They seem to be an adventure magnet, because they always seem to land right in the middle of it all despite their best efforts to have "a quiet holiday"... and if there's any treasure to be found then rest assured these kids will stumble upon it!

Each adventure takes place in a remote setting – an island off the coast; a castle on a hill in Scotland; a valley in a distant, deserted land; more islands of the coast; a mountain in Wales; a ship cruising around the Greek islands; a circus in the country of Tauri-Hessia; and finally a river in a faraway, ancient land.