Like people above said, it's going to depend on a lot of things (also, taking care of basic survival on your own while also hiding from other humans will not be easy, even in woods they know and have been trained to survive in. If they haven't been it will be a lot of living day to day just trying to eat enough to look for more food. Hunter/gatherer can be a great lifestyle where there's plenty to eat and do - if you're part of an established community that can support and train each other.)

But I just want to toss in - depending on the needs of your story and why you have them hiding in the woods, traditionally people kidnapped by fairies have time dilation issues. So if you wanted to skip all of this you could totally have the fairies take them Year One and then they show up again Year Three thinking only a few weeks have passed. (Whether they physically aged during that time would be up to you - or if you want some real fun you could have all of the missed physical development catch up with them suddenly right after they return, which happens sometimes in the stories too.)