Password protecting a folder in Windows 10

There isn't a built-in folder password in Windows 10. The cleanest fix on a shared family PC is to give the kids their own Windows accounts (standard, not admin) and keep the documents in your own user folder. They can't open another account's Documents without your password. If you want an actual password on the files instead, 7-Zip can put them in an encrypted archive with AES-256 and a password. Just make sure you remember it, there's no recovery.