Folder Guard (bit costly) @ Folder Guard: Password protection software for Windows (winability.com)
Let's backtrack a little: why does your questioner want to password-protect a folder? If, for example, it's simply to protect from prying eyes then you could teach them about Windows' permissions system and having different accounts for each user.
I'm not able to go visit them and teach them about permissions.
How safe is one drive as its a cloud? I never use clouds to store my own stuff.