I used to believe as a child that cats were the girls (since they were kinda prissy and feminine) and dogs were the boys (since they were kinda rough and tuff) and if they had babies cats were born for the female sex and dogs were born for the male sex.
A childhood belief about cats and dogs

others believed things like this
- My sister and I thought cats and dogs were the same animal, the dogs were male and the cats were female.— Paul
- I used to believe all dogs were male and all cats were female. I still call dogs "boy" and cats "girl." — Kelly F.
- I use to believe that cats and dogs were the same species; cats were girls and dogs were boys.— poopcrystals
- I used to believe all cats were female and all dogs were male.— Sabby
- I used to think that all cats were female and all dogs were male. — Annalisa
- i used to believe that all cats were female and dogs were male!Anon