If you've ever seen the film My Sister's Keeper, you probably already know what a "glass child" is. It is a term for the siblings of children with illnesses who tend to be ignored or neglected because of the high needs of their brother or sister. They're called "glass children" not because they're so fragile they can shatter but because their parents tend to see right through them and don't consider their needs as important as their siblings.
One grownup glass child recently shared her story on Reddit, and it's heartbreaking to read. She was the only one of her five siblings who did not deal with severe health issues. Her parents completely ignored her and consequentially formed a "found family" with two friends who grew up in a similar situation. Now that she's an adult, her parents are trying to get back into her life but are failing to know the most basic facts about her.