Hello and welcome to healthcare magic forum.
The above mentioned condition means that the pelvis of left kidney
is little bit dilated and its exact importance lies on the fact that why your son of age 15 days was advised to undergo sonography? This condition usually occurs due to blockage in distal passage of urine like ureter
. As it is mild at present no specific treatment would be required at present, but there should be follow up sonography done to have watch on progress of the condition.
Best wishes for health of your son.