From ages approximately ages 10 to 14, I had HUGE growth spurts (at one point, growing 6 inches in 3 months). The "growing pains" in my arms and legs were sometimes extremely painful. I was convinced that the pain was because I was dying from some horrible disease. I never told my mom about them because I knew how upset she would be at her youngest child dying, or at very least, it would bankrupt her from the medical expenses. There was nothing ever wrong with me. :)
A childhood belief about getting older

others believed things like this
- I used to think that growing pains meant that a tomato plant was growing in your stomach.— Annette
- I used to beleive that all pains were headaches. So for example, I had headaches in my stomach, legs and arms.— James
- I spent ages wondering what a bart ender was as a child without realising that it was actually bar tender.— Heather
- I used to beleive that a catacism(spelling?) was an extremely painful Christian version of a bris.— Mike
- When I was a child I used to believe that the things in my room became smaller but it was me who was growingAnon
- We told our little sister that she had a long bushy tail and she fully believed us for ages!!Anon