@Riger : Depending on how many monsters there are, requiring them to know the abilities of all of them (even if only up to your rank) is not reasonable.
Normally an adventurer would encounter a monster from a quest taken at the adventurers guild, or in a dungeon, and able to research the individual monsters in the area before hand. These kids were passing through town, and it is a monster not commonly found there, so that resource is not available.
@mage_goo : The soldiers are only going to focus/study up on the monsters that are normally found in their area, there are not normal to the area so they have an excuse. While an encyclopedia would make sense, the likely size required, combined with most of the information being in the hands of non-scholars makes it less likely to exist, or be cheap enough for the average joe to be able to read it. It would not surprise me if the guild has one, but it is a resource for the guild and adventurers only. Keep in mind how much knowledge has been lost because it was only ever passed on master to apprentice rather, than written down, because they did not want their "trade secrets" getting out.