So, of the two JavaScript, because motivating them to program is more important than anything else if they have no prior knowledge. javascript has great tooling and faaar less hurdles to get something going then C. Personally i'd go with TypeScript if it has to be anything in this family of languages, because making them think of types early on is helpful when moving to anything more than little web apps. If any other languages are considered, i'd go with python with type hints because it forces you to format your code somewhat readably (believe me, i know that it's possible to write unreadable python code) but is really low on boilerplate, has great tooling (at least third-party, use uv) as well as stellar IDE support and allows for multiple different paradigms to be explored.