Might as well practice hard pen. Children's control over writing brushes is not very strong. It will be more difficult to use the brush at first, and it will be more difficult to hold the pen. Moreover, the number of literates is limited, which has certain obstacles to learning soft pen calligraphy. It will be much easier for children to learn writing brush around the age of ten in the third grade, and it will have good results.
Learning hard pen should also pay attention to docking with textbooks. Do it right away. Develop good writing habits.