I used to think that the letter W had a sound that you'd repeat U two times. I was three and would pronounce, for example, watermelon: "U-Umelon". (double u...?)
A childhood belief about speaking

others believed things like this
- If you eat watermelon seeds a watermelon will grow in your tummy and vines will come out your earsAnon
- when you eat the seeds from a watermelon a watermelon will start to grow inside your stomache.Anon
- I used to believe that if you ate a watermelon seed you would grow a watermelon tree in your stomach!!!— Eskimo
- I use to believe (thanks to my Mom) that if I swallowed a watermelon seed a watermelon would grow in my belly.Anon
- i used to think if you ate a watermelon seed then after a while you'd become a watermelon
— olga british-girlyman - When my sister was about 9 or 10 she used to pronounce "chaos" like "chows"Anon