My first rememberable experiences with urinals began at school, and those were the long metal ones designed for multiple people to use at once.
So when we went out for dinner one night, I went to the toilet, and for the first time I remember, I saw individual ceramic urinals, never seeing these before, I assumed these 'smaller toilets' were for 'babies' and the toilet cubicles/stalls were for grown-ups.
Later in the night I returned to the toilet shocked to see my grown up uncle among other people using the 'baby's toilets', I persuaded my slightly younger cousin, who also had to use the toilet, to use use the 'normal' toilet like a grown-up.
Nowadays - I coincidentally never use urinals, not because I believe they are the 'baby's toilets', but because I much prefer to do my business in privacy - even though I stand up when doing so.
A childhood belief about general

others believed things like this
- I thought that toilet paper was bread and by puting it it the toilet i was feeding the ducks at the bottem.— Gringo
- I used to believe that monsters lived in my toilet and they ate my poop and urine when i flushed the toilet.Anon
- I used to believe that if I flushed the toilet before I showered, I would take a shower in dirty toilet water.— Chris D
- I used to beleve when i was 4 that the flush on the toilet was to wake up toilet monsters.— Millie
- I used to think if I left the toilet seat open my cat would get flushed down the toilet.— G
- I believed the urinals in port-o-potties were sinks.Anon