Should the funeral prayer for children involve supplicating for them or for their parents after the third Takbir, and what is the ruling on increasing the number of rows in it even if they are not full, and is this from the Sunnah?

There is no specific supplication authentically reported from the Prophet, peace and blessings be upon him, for a child in the funeral prayer. Rather, he used to say: "O Allah, forgive our living and our dead, our young and our old." It is recommended to supplicate for the child and their parents in the funeral prayer by saying: "O Allah, make him a forerunner for his parents, a treasure, a predecessor, and a reward. O Allah, make his passing weigh heavily in their scales and greatly increase their rewards. O Allah, place him in the care of Abraham, join him with the righteous predecessors among the believers, protect him by Your mercy from the torment of Hellfire, and grant him a home better than his home, and a family better than his family."