@dope0420:
The kid being a kid is only half the reason Ja took action.
The other half is that those attackers refused to explain the situation.
If they would have stated a justified reason like "That kid actually killed someone." or "That boy stole a really expensive / important item." followed by "If you do not believe us then you can come along with us as long as the kid won't escape." then Ja would have likely agreed to look at the evidence they have.
And once shown the evidence he would not have allowed them to kill the boy but would have investigated / tried the boy with his own dragonic powers to confirm the truth.
As a result he would then have found out:
A) That being is not actually a child and just poses as one.
or
B) The child is actually really a child but possessed by an evil existence like an evil spirit or so.
In case A Ja would have probably immediately dealt with that trickster and in case B he would have looked for a way to exorcise the evil being from the boy while watching over the boy personally to not let that evil being escape.
So in the end the fault lies with those adventurers not explaining the situation and hence appearing like some slave hunters that try to attack an innocent orphan.