Just a brief introduction to the story:

Kim Sunggyu - 8 year old
The boy who was sold to the Nam's along with his younger brother. He had a hard life in his past, serving his parents and looking after his little brother at the same time.

Kim Myungsoo - 6 year old
The boy who was sold to the Nam's with this older brother. He treated Sunggyu as his saviour, his father figure in his life since his parents do not bother with him at all.

Nam Woohyun - 6 year old
The young master of the Nam's. He used to be very obedient and sweet but he witness his older brother's death which caused him to change for the worst. His previous butlers were chased away by his toublemaking skills. His older brother died in a car accident 2 years ago while the family was on a trip to Jeju Island.

Lee Howon/Hoya - 7 year old
The eldest of the Lee's. He's 7-year-old but is quite mature for his age.

Lee Sungyeol - 6 year old 
The middle child of the Lee's. He's the ball of sunshine due to the influence of his elder brother's butler. His butler recently quited because of family issues.

Lee Sungjong - 3 year old
The baby of the Lee's. He's absolutely shy but scares his brothers a lot when he cries. 

Jang Dongwoo - 8 year old
The butler who grew up together with Hoya.

Yoon Doojoon - 8 Year old
The butler of Sungjong ever since the younger was born.