Question:
Can children ride their bikes on Shabbos?
Answer:
Children should not ride on a bike on shabbos similar to adults (see the following post https://dinonline.org/2017/04/25/b-s-d-riding-bicycle-to-shul-within-an-eruv/ ), however a tricycle is permitted.
Sources:
Be'er Moshe 6-16, Children in Halacha pg 138.