To engage in reasonable exercise for primary school students, it's essential to consider their age, physical development, and interests. Firstly, choose exercises that are suitable for children, such as running, jumping rope, playing basketball or soccer, swimming, and gymnastics. These activities promote cardiovascular health, strength, and flexibility.

Secondly, ensure the exercises are fun and interactive. Involving games and competitions can make workouts more enjoyable and encourage kids to continue exercising.

Finally, remember to warm up and cool down before and after each session. This reduces the risk of injury and allows the body to adjust to the activity.

In summary, by selecting appropriate exercises, making workouts enjoyable, establishing a consistent routine, and warming up properly, primary school students can engage in reasonable exercise that benefits their physical and mental well-being.