It appears unusual, but I never believed all cats to be female and all dogs to be male (even though I'm German, and you neutrally say "die Katze" (f) and "der Hund" (m) in German). I was half convinced our dog could talk, though. I distinctly remember imagining he did on one occasion.
A childhood belief about cats and dogs

you weren't the only one
215 of you believed this
- I used to believe that cats were all female and dogs were all male.— Rachel
- that cats were only girls and dogs were only boys. I definetly didn't get the whole reproducing thing yet.— Jamie
- i used to believe a dog was the male version of a cat.Anon
- I believed that all cats were female and all dogs were male. — Biologically confused
- i thought cats were girls and dogs were boys. Anon
- i used to believe that all cats were female and dogs were male!Anon