The Ghost Child, yet to fully grow, simply had no way to stop Wei Jing from leaving. The only reason Yang Jian was intercepted was because of the rotten Dead Man's Head; currently, the Ghost Child wearing the Ghost Shroud mostly possessed the ability to resist the harm caused by other malevolent ghosts.
Therefore, even if Wei Jing suppressed the Ghost Child, he couldn't kill it, and without continuous suppression, the Ghost Child could come back to life again.
This point was crucial.
The reason Yang Jian chose the Ghost Shroud for the Ghost Child to wear was out of a concern that the Ghost Child was not a true ghost and could potentially be killed.
Previously, in Dachang City, he had killed a Ghost Infant of the Second Stage.
As for why he didn't allow the Ghost Child to control other ghosts, it was to prevent the Ghost Child from becoming uncontrollable, so Yang Jian was very conservative in his choice of ghosts.
Now, the conservative choice had its effect.