Not sure about their Pokemon, but when you beat one of them they could give you a Sitrus/Lum Berry
(You called them Forest Kids, so i figured, lol).
Please please
please, let's call them Cabbage Patch Kids. Or Berry Bush Kids, if copyright's a problem.
Anyways, we need to have an idea about the forest and what aspects of the game are introduced in it. Remember Eterna Woods in D/P/Pt where you team up with Cheryl? I have an idea for that, but first let's talk about something this Forest should be known for:
Berries.
As we know, Berries can play a large role in competitive play, but we never really see them used in a play-through since most people can't be bothered to farm up a backlog of berries for every goddamn battle. What I have in mind are two items: A Key Item called the
Berry Breeder, and a held item called the
Bottomless Berry Bag. Yay alliteration! The Berry Breeder has a slot for every berry in the game, and the kicker is that it creates 1 berry of every occupied slot every 512 or 1024 steps.
This is just a placeholder number, so you can change it to anything for balance purposes. The Bottomless Berry Bag is linked to the Berry of your choice in the Berry Breeder, and a Pokemon can hold the bag to gain use of the selected Berry in the bag once per battle. This allows players to try out things like SubSalac or other strategies without running low on supplies, and having infuriating downtime between usage of said strategies. I suppose you can also have a separate tab in the Berry Breeder that allows you to cross-breed Berries, with the same mechanics as those in XY.
Now, how do we get this item as related to the story?
We will get this pouch in a certain grotto (not Hidden Grotto like BW2) that can be found near the beginning of the forest. Within this certain 'secret' area, you find a colourful clearing, filled with Berry Bushes and Berry Trees of nearly every type. In the middle is a giant pile of berries, and 3 Munchlaxes playing around it. Smack in the middle of the pile is...well, whaddaya know, it's our first Gym Leader, making snow angels in the berries, having the time of her life. (Gender is irrelevant here, but I figured it'd work better with a female Gym Leader.) Upon getting close enough, she gets up with a start.
"Aww crap. Hey look, kid, this is...this is nothing you should be worried about. Just turn around and pretend you didn't see anything.
...Pretty please?...
...Hey, don't give me that look! Being a gym leader's hard work! As a Gym Leader, you're not just the head of the Gym, you're also a mentor! Do you have any idea how many people try to battle me and ask me for help choosing their team? Do you know how many people chat me up on my IRC for battling tips? I deserve some time off! Fine, if you don't tell anybody, I'll give you a sweet new pair of items." [YES/NO PROMPT]
[Choice of NO]: "If word gets around that I spend my free time frolicking in berries like a Munchlax, I will
end you. When you come for that badge, I swear I'll use my personal team instead of the Gym-sanctioned one." [LOOP PROMPT UNTIL CHOICE OF YES]
[Choice of YES]: "Good. Here's a
Berry Breeder and a
Bottomless Berry Bag. [Items get!] Put a bunch of Berries in the breeder and watch them grow as you walk. You can select a type of Berry with that bag and let your Pokemon hold it. As long as you have a stock of Berries, you never have to re-give your Pokemon the same Berry! Useful, huh? If you want berries, you should look around this clearing. There's plenty."
Around the clearing, there should be many accessible Berry Bushes that you can farm up. Perhaps, for inventory's sake, you can provide 10 of each berry from each pick-up. As for what kinds of berries, we can choose quite a few. Sitrus, Lum, Yache, Occa, Shuca, Chople, Chesto, Salac, the list goes on. I'm not sure which berries are most competitively common other than Sitrus, Lum and Chesto, so I'll rely on feedback from you guys for that.
Upon trying to leave the clearing after talking to Gym Leader (whose name has not been decided): "I should be heading back to the Gym anyways. Mind if I tag along? Ah, who am I kidding, you don't get a choice." [Bossy Gym Leader chick joins your party!] "Hey, I heard you call me that! Hmph, see if I go easy on you for your badge."
This is also a good place to give a quick peek into Doubles, although it may not be a very intuitive peek. Perhaps have some of the Double Battles be Pineco and Ferroseed with Protect and some attacks. If Pineco gets Selfdestruct or Explosion that early or something, it can show you the negative effects of spread moves in Doubles as well. If you meet Team Luck-Sack in this forest as well, we can make it a Double-Bidoof Moody Protect Bonanza (tm).
Upon leaving the forest, and reaching the next city: "I don't wanna see another Protect for a good, long while. Anyways, we're here! You heal your buddies back up and see me in the Gym. I'll be waiting for that challenge!"