Parentification

Parentification occurs when a child in a family has to take on the role of an adult. This usually happens when one or both of the parents are unable to take care of themselves because of a disability, so the child becomes their caregiver. It could also be due to the child having to care for younger siblings, or disabled siblings, while their parents are at work.
In some situations where there is abuse in the family, a child might also become the emotional caregiver of a parent, supporting them through traumatic incidents and even protecting them. 
Parentification is very damaging for a child, who ends up missing out on having a childhood.