Yes — children's sumo is actively practised both in Japan and internationally, and serves as the main pipeline for future professional wrestlers.
In Japan: Elementary and junior high school sumo clubs exist throughout the country. The All Japan Youth Sumo Championship is a prestigious event. Many professional wrestlers began sumo before age 10 — Aonishiki started at age 7 in Ukraine.
Internationally: The International Sumo Federation organizes junior world championships with age categories starting from under-15. Countries like Mongolia, Ukraine, Georgia, and the United States have active youth programs that have produced professional wrestlers.
Entering professional sumo: The minimum age to join a professional stable is 15. Young wrestlers with strong amateur records can join at the makushita tsukedashi level, skipping the lowest divisions. Most professional careers begin between ages 15-18.