Children believe what they’re told. Doesn’t matter how unrealistic or uninformed the beliefs are, if you tell a child to believe trashcans are a portal to another dimension where trash monsters live, they’re very likely to trust you, because they haven’t yet had the life experience to think critically about their reality. Going further, they’ll hold onto things that are less easy to disprove to oneself. It’s very hard under capitalism to disprove indoctrinated ideals without the sources required to prove that another world isn’t only possible, but is logical.

Children just don’t understand how small the chances of striking it rich are in capitalism, maybe there is some propaganda to it but for the most part, it is the stupidity of childhood. they te4nd to see people like bill gates and jeff Bezos and think how am I any different from him? if he can strike it rich I can too, of course since they’re kids not knowing that in order to do that they will need to steal the surplus labor value of others.

Check out Antonio Gramsci’s theory of cultural hegemony.

Essentially, those in power (i.e. in capitalism, the bourgeoisie) establish norms and values to justify/rationalise the current power structure. In other words, the capitalist class use all their available assets (primarily the media and state) to create a sort of mythos that keeps them in power. If everyone believes “hard work = success” , “capitalism is the best system we have” , “communism is good in theory but always fails” and other rhetoric I’m sure you’ve heard before, then they will essentially “consent” to capitalism. Think how many working class people you know who whole-heartedly believe they will ‘make it big’ if they just work hard to see the point I’m getting at here.

On to your question - simply put, the minds of children are considered far more malleable than adults with strongly-formed opinions. Why do children believe they will be rich? Because of cultural hegemony. Any interaction they have with economics likely amounts to their parents telling them “hard work pays” or similar mantras. Depending on the ages of the children in question, perhaps they have already experienced this kind of inodctrination in school, being told “inspirational” stories about the “hard work” of billionaires that got them to where they are today.