Hello, My Son Was Born With Hydroneprhosis With Calyx Measured

Hello, my son was born with hydroneprhosis with calyx measured at 9mm and pelvic measured at 1.38mm on the left side. Both kidneys showed normal size, echogenicity, cortial thickness and good corticomedullary differentiation.
Now, my son is 4,5yrs, and the result is - mild dilatation of the left pelvicalyceal system extending into the left ureter proximal to 1 cm ureterocele at the left UV junction with no definite left renal calculi.
Looking for the second opinion. Was told to do a follow up after some time.
Thank you very much.