The Sand Creature.

Piesočná potvorka (lit. The Sand Creature) is a 1985 Czech television miniseries based on Edith Nesbit's 1904 children's novel Five Children and It. The four Majer children—Janka, Braň, Cyril and Vladek—spend holidays together at a cottage, with their aunt Marta, who takes care of them in their parents' absence. One day, the older children decide to dig in an old sandbox and find an ancient wonder: Brontofusika, a prehistoric creature that can grant wishes. So Janka wishes that everyone would be as beautiful as the heroes from a fairy tale. It happens. No one recognizes the children in this disguise, not even their own aunt, which brings a lot of funny but also unpleasant situations. But the magic only works until sunset!