I doubt a 12 year old would know/care about that though. They would notice that almost everyone had a car, there were no shortages in grocery stores, houses were much bigger, etc.
You start also to notice that there are no differences in the propaganda narative between your home country and the country you visit. And that some people live on the streets. In the end you need to choose your masters.
Well, it's not that difficult to understand why (the US brand of) capitalism is harmful by wandering around the US for a while.
... problem is, it may not help convince you that Stalinism / "Actually existing Socialism" is the answer. (In case you don't recognize this term: https://en.wikipedia.org/wiki/Real_socialism)