[TOMT] [Cartoon] [2000s] Cartoon about little forest people

When I was a child, I watched a cartoon about little people from the forest. They lived on the trees. The main hero was a little boy from this forest. Once he went away and befriended a human, who was a grown-up person. I remember one moment: this boy stood on the table in the house face to face with two human children: boy and girl.

I also remember a man from the forest. I guess, he was that boy's grandfather. He was really angry, when the boy vanished.