Hydrocele: This condition is characterized by the accumulation of fluid around a testicle, leading to swelling. It's common in infants and young children due to a patent processus vaginalis, which allows fluid to move between the abdominal cavity and the scrotum.

Epididymitis: Although less common in this age group, epididymitis (inflammation of the epididymis) can occur, especially if there's an associated urinary tract anomaly or infection.
Testicular Torsion (partial or intermittent): While testicular torsion is more commonly associated with acute, severe pain, partial or intermittent torsion can present with swelling and less severe pain, making it a consideration in this age group.
Varicocele: A varicocele is an enlargement of the veins within the scrotum, similar to varicose veins. It's less common in young children but can cause swelling.

Testicular Torsion (complete): This is a surgical emergency. Even though the presentation might not always include the classic severe pain, any suspicion of testicular torsion warrants immediate medical attention due to the risk of losing the testicle if not treated promptly.
Appendix Testis Torsion: Also known as a torsed hydatid of Morgagni, this condition involves the twisting of a small appendage on the testis, leading to ischemia and potentially severe pain and swelling.

Testicular Cancer: Although extremely rare in infants and toddlers, testicular cancer can present as a painless swelling of the testicle.
Spermatic Cord Torsion: A rare condition where the spermatic cord (which contains the vas deferens, blood vessels, and nerves) twists, cutting off the blood supply to the testicle.
Scrotal Hematoma or Hematocele: These can result from trauma and might present with swelling, though they are less common in non-ambulatory children without a history of injury.