Tulunk Village

Through searching Taobao, I managed to find a couple of bootlegs of Devil Children out there.

There's a bootleg of Red Book, with a different chunky font for the 'Gameboy' text on the left side. The boxart also looks poorly printed from the official Japanese one: http://item.taobao.com/item.htm?spm=11029f*x.3-iLz8.h-4josD&id=5814262221&

There's a bootleg of Black Book, also with poorly printed boxart, but this time the logo has been translated into Chinese and fills up the bottom half of the box. There's also added Chinese text in the top right corner of the box: http://item.taobao.com/item.htm?spm=11029f*x.3-iLz8.h-4josD&id=5814189535&

At first, this particular bootleg's boxart makes it look like it would be a hack of a Pokemon game, namely Pokemon Gold, but it turns out it's a hack of Devil Children Black Book from the screenshots on the back, and it's been translated into Chinese: http://item.taobao.com/item.htm?spm=11029f*x.3-iLz8.h-4josD&id=2024119741&

There's also a Chinese bootleg of White Book (Shiro no Sho) out there too, but unfortunately I don't have the link.

Some unnofficially (i'm assuming) translated guidebooks for the games exist too and appear to be based on the Japanese guidebooks:

Red/Black Book guide: http://item.taobao.com/item.htm?id=6757508948
Demikids/Light/Dark guide: http://item.taobao.com/item.htm?id=6285564174
Fire/Ice guide: http://item.taobao.com/item.htm?id=13274049116

http://item.taobao.com/item.htm?spm=11029f*x.3-iLz8.h-4josD&id=5814262221&

The screenshots of this remind me Telefang a lot...
Excpecially the Tree and the kids with a gun (I think?) in the orange screen. He seems Kai during the first met in the game.

Devil Children has a very different style from Telefang, but they're both gameboy color games so the graphical capabilities might be similar. They're not related though. Devil Children is made by Atlas. The kids with the guns are Mirai Kaname and Setsuna Kai, the two protagonists. They use the guns (the Devilyser/Devil Riser) to summon demons in the game.

Also, I can't find the tree you mentioned on any of the boxes. The only thing that looks somewhat like one in the link you posted, is the brown dragon creature on the right hand side of the box. Is it possible you might have mistaken it for a tree? The boxart is rather dark on the bootleg and it makes his wings look like branches.

Uhm...I mean in the last screenshot, the green round thing owo
http://p7.images22.51img1.com/6000/soundgarden1/72a2541b19e3086d34ae1523e54b44a3.jpg

It's actually a building with a green roof, but I can see why the low resolution makes it looks like a tree. The two 'kids' are actually Mirai and her griffon partner, Veil ^^

EDIT: I found another bootleg that has Aka no Sho's boxart but Kuro no Sho's boxart on the label: http://item.taobao.com/item.htm?id=6752161474