A childhood belief about speaking

When I was about 9, I had a 2 year old baby sister and a few months old baby brother. Sometimes, I would play with them and then they gurgle and mumble stuff and look at each other. I used to think they were communicating in some secret baby organization language, and it made the most sense to me. I asked myself: "How come I don't remember those times when I was a baby?".
Then I came to the conclusion that they had a secret Baby organization in some base and that they were members of it. I thought that when members got too old, they erase any memory of the organization.
From then on, I started interrogating my baby sister and brother whenever my parents would leave them alone with me.