Context · Games
Steam is where most PC gaming happens, and it is a store, a chat app and a social network at once, which means the parts worth checking are not the ones a parent expects.
It is a social network as much as a store
Steam has friend lists, profile comments, group chats and direct messages, and a child can be contacted by someone they played one match with. Families who thought about which games to allow have often not thought about the messaging layer running underneath all of them.
Community content is not reviewed like games
Alongside official games there are user-made mods, workshop items and community hubs, and those do not go through the same checks. A game that is fine for a twelve-year-old can sit next to community content that is not, in the same window.
What Family View actually does
Steam has a Family View that can lock the store, friends and community sections behind a PIN while leaving chosen games playable. It is genuinely useful and almost nobody turns it on, largely because it is buried a couple of menus deep in the settings.