7 Princess
The group consist of seven members and range in age from 7 to 11. Their format was similar to Japanese groups since they had different Generations of members. If fact Mooi from GP Basic was a member. They debut in 2004, they are now disbanded. 

TROTTY
A five member girl group. [disbanded]

Girl Story
Consisting of 4 members, Kim Hye In (9), Lee Yoon Jung (9), Kim Yuri (10), and Kim Chae Young (11). They debut in 2010 however they are no longer active, but this doesn't mean they disbanded. They debuted with an auto-tuned song; "Pinky Pinky".

Sweety
A nine member mixed group with eight girls and one boy, consisting of the team mascot, Yujin (7 years), including the main vocal Kyungbin (13 years), Hyemim (age 14), Jimin (12), rapper Junheon (11 years old) and Seungmi (Who is now know as Janey of GP Basic) (11 years), sub-vocals and choreography, Ye rin(age 14), Jini (11 years), Youngeun (age 14). Janey from GP Basic was in this group before she was in GP Basic. They debut in June 1, 2008 and released two single in that same year, they have been inactive since then and are presumed disbanded due to low funds in their company; Yoowon Entertainment

Ryanghyun Ryangha
Consists of two twin brothers who debut when they were 12 years old. They debut in 2000 and released another single in 2004. They are presently inactive as they are in the military for their two mandatory military service. 

Uniteen
A mixed group that has ten members, I can't find a picture of their group but here's a link to their music video. Also Janey from GP Basic was also in this group before she was in GP Basic. They debuted in 2007 as Unicef Korea's project group
[youtube]http://www.youtube.com/watch?v=KivAido61_8[/youtube]

If you want to see all the other groups MV's I've added their profiles to GoKpop.

Cutie-L [They debut in 2010]

4Kids [They debut in 2012]
A mixed group with three girls and one boy, I'm not sure of the ages, I'll update when I know.

KIDS RULE THE WORLD X]]]