My daughter started jiu-jitsu at 8. The confidence is what every parent notices first. A quiet certainty that changes how she carries herself. She doesn't get pushed around at school, not because she fights but because she carries herself like someone who doesn't need to prove anything.
Martial arts teaches problem-solving under pressure, losing gracefully, discipline without rigidity, and body awareness based on capability not appearance. For self-defense: most real-world altercations end on the ground, and knowing how to control or escape is practical knowledge.
Injury rates are lower than soccer, gymnastics, and cheerleading. Most gyms offer kids' classes starting at 5-6, with ages 7-10 being the sweet spot. Give it three months before deciding.