As PerfectDeath noted, the child thing might be a binding to the dungeon king thing. But I also that this is just an excuse as their main motivation seems to be bullying/destroying her by sullying her.
Actually this ""oh so pure and innocent" stupid dumb fk of a princess" is the only person in this chapter, that made any sense. This sign in the dungeon entrance also confuses me. How should a so crude and fault-prone plan work? By a chance of 1:100?
1. Maiden stops by being confused.
2. She gets hurt.
3. She moves into the dungeon.
4. Solders also get confused, but interpret this in a favourable way by thinking the dungeon has been cleaned out, so that they let their guards a bit down.
5. Soldiers follow her into the dungeon.
I'm okay with step 5 and somehow with 3, but what if:
1. There are soldiers behind her! I wouldn't have stopped and read that sign in her place and in first place.
2. She was never in danger? Those arrows could also have hit her in the neck, backbone, the back of her head or punctuated her heart. Ever heard of poison? Some kill within seconds. What if her leg would have been hurt in a way immobilising her?
3. The sign might have confused her to NOT enter the cave. ;D
4. That sign looks suspicious. Better be on alert.
And every character is okay with that plan? They even figured it out on themselves? And the princess is the dumb one? The author tries to hard to be clever. He constructs plans like "incredible machines" and let the characters state how cunning those plans and how deceiving those political intrigues are. The fundamental idea is great. Building a dungeon into a city. But in the end it's just another harem story with not too bad bitching among the girls and a bit fantasy world setting around it.