A bias or discrimination against younger people. This perhaps makes people dislike their childhood. This is due to the assumption that children have less knowledge and need to be protected. Children technically lose a lot of freedom, for instance, to school or their parents. Instead, perhaps we should judge their ability.
Being expected to function like adults while still being affected by the education system, and in much more intense forms than before. Their brains are not fully developed yet, and their lack of sleep impairs decisions, so I think that we shouldn't hold them up to adult standards!
For instance, in most places, people under a certain age cannot vote. The argument is protection. But it also restricts freedom, even when it does not harm others, and human brains develop at different rates: There are stupid adults and smart children! Though pragmatically, it would be ridiculous to examine a human brain to determine its maturity, so that's why it's this way now.