Kidney stone in 12 month old baby

My 12 month old son had visible reddish brown colored urine in his diaper so went to the doctor. A large amount a blood was found in his urine sample. An ultrasound found a 5 mm possible kidney stone in his kidney.

How do baby's get kidney stones? I nurse on demand and have given him water since 6 months. He eats solids but he's never had any meat, dairy, or refined sugar.

He doesn't seem to be in any pain in his kidney area.

Are there any natural ways to treat, help resolve this issue?