Hi Miyuki,
Thank you for your excellent explanation on the three types of Japanese Onomatopoeia - I realised Japanese kids or children songs use a lot of onomatopoeia too:
https://www.youtube.com/watch?v=bgFz0izvZO4
Kuchuu Kuchuu, Shuuwa Shuuwa seems to represent the motion of brushing teeth, I guess a form of giongo?
And yes, now that you mentioned it, manga has a lot of onomatopoeia too!