Dospeláci muzou vsechno (1970) on Netflix

Plot summary

Mísa is eleven and lives with his father, where he has his own duties around the house. The grown-ups bring him endless trouble, and he wishes he could be an adult already. After a failed attempt at the dishes, he goes to his father's research institute, where work is under way on an important invention. The father is trying to develop a substance meant to fatten poultry and other animals and so ease the struggle against famine, but his experiments have produced only a shrinking agent. Once his father has left the laboratory, Mísa mixes the ingredients into the growth substance and drinks it, and at once he is an adult.