This seems a rather awkwardly low-level quest to be sending us on.
I mean, I understand that you probably have developments waiting for us, but if I were IX, I would raise an eyebrow at the quest as it is currently being offered, but seeing as that is not within IX's nature, I'm having a bit of trouble reacting here.
On the other hand, if someone went missing "recently", I assume some time has already passed, perhaps a day or two. For the level of danger a child might find him/herself in that amount of time, Cobalion's quest doesn't seem... very urgent.