* In high school: Many parents continue to provide financial and other support to children still attending high school, even if they're 18. Legally, this is generally voluntary.
* Dependent due to disability: If a child has a disability that prevents them from being self-sufficient, parental responsibility can extend beyond 18, sometimes indefinitely. The specifics depend on the nature of the disability and local laws.
* Financially dependent (with caveats): Even without a disability, if the child is still financially dependent on the parent, the parent may have some continued responsibilities. However, this is less a legal obligation and more of a social/familial expectation. The parent isn't legally required to support an able-bodied 18+ year old unless it's part of a court order (e.g., child support agreement extending beyond 18).
In short: Legal responsibility typically ends at 18 in most jurisdictions for basic care and support. However, practical and sometimes legal responsibilities can extend beyond 18 depending on the specific circumstances. The extent of these responsibilities is not a simple yes or no answer but varies widely by location, the child's circumstances, and the specific type of responsibility in question.