Hyrule: Total War is a conversion for Medieval 2: Total War. A vast majority of the iconic races from the Zelda universe have been represented as armies that the player can assemble, command, and ultimately use to destroy their enemies. The Hero of Time has chosen to return to the past, a choice that ultimately has ruined the charts of history and sent Hyrule into chaos. Major wars that were already decided have unmade themselves, allowing fallen armies a second chance at these critical events in Hyrule's history. This is where you, the player, comes in.
Wait... I thought the Kokiri couldn't leave the forest, or else they would turn into skull kids
If you plan to play this then you need to learn real quick that this DOESN'T follow the official lore.
I remember it along the lines of they died, plain and simple but if they died in the lost forest or other inhabitants they turned into Stalfos? and/or skull kids. My info may or may not5 be 100% accurate.
My version is that they can leave the forest, and in the process, start aging to whatever age they would be at if they were Hylians. The reason they never leave is because the myth that they die if they leave is perpetuated by Mido to prevent emigration and eventually, the loss of whatever power he wielded in the first place.
And THIS is why the game would never be released if Nintendo decided to make it. The media watchdogs would have a field day over the depiction and deaths of what is essentially child soldiers, something that may be the reason Saria is not, nor may never be in Hyrule Warriors.