My son has urine reflux on both his kidney on a renal ultrasound. Is that bad?

Varies. The urine collecting system is supposed to flow out, not back & reflux describes back flow. Two issues have importance;chance of infection going up to the kidney from the bladder& pressure stretching open the collecting system. Low grade reflux will often disappear within a year or two, high grade reflux may require surgery.Discuss your kids findings & explore your options.