From 1998 to 2009 Aerts was a member of the famous and successful girl group K3. In 2009 she decided to stop being a member of K3 and to start her solo career. Her first song, named "Zumba Yade", was made in cooperation with Unicef. Aerts spent for each bought CD some cents to Unicef. She sold more than 10,000 CDs in Belgium and the Netherlands. In 2010 Kathleen became a member of the "Ketnetband". In 2010 she also decided to go back to children's music. So she made a song, named "Boerderij blues" (en. Farm blues). She will make just three other songs for children. Since 2007 there is a wax figure of Kathleen Aerts in the museum of Madame Tussauds in Amsterdam.