Why Do We Remember things From Our Childhood?

[abaris]

I was told that the body takes seven years to completely replace every cell. So all the cells I had seven years ago are gone.

First, that's an urban legend I grew up with too. Science has moved beyond that since.

Second, if it were true and you would forget everything you knew before your cells changed, you would pretty much forget who you are every now and then. It doesn't work that way of course and we do remember many things from decades ago. Although these memories should always be taken with a grain of salt, since we tend to reinvent them in parts. It's also true for witness statements where everyone saw something different. There have also been some recent experiments where scientists virtually created memories for their pro bands of things they never experienced in reality. And yet they all bought the created version.