Qin Chuyu's foray into the palace with his little buddies was with the consent of his sister-in-law, the Prince's wife, who had made all the arrangements so that his identity would not be revealed.
The entrance to the Imperial Palace has three doors. The largest and tallest door in the middle is generally only used by the Empress Dowager, the Empress, and the Crown Prince's couple. Ministers usually use the side doors on either side.
Qin Chuyu, as the legitimate royal son and brother of the Crown Prince, is also allowed to use the middle door.
Xu Zhuzhu, who is a year younger than Qin Chuyu and is seven years old this year, hasn't visited the palace before. But he knows that his father goes to court every day through the side door.
When he entered through the central door, he instantly felt he could brag about it to his father when he got home.