How to Protect the Data on Your Laptop
Make sure you have your own user account set up on your laptop, even if you're the only one who uses it—not only will this keep the kids from messing up your browser bookmarks when they want to play games, it'll also stop anyone else from accessing it. Even if your laptop gets stolen, if there's a password-protected user account on it, there's not much a thief can do beyond resetting it and wiping the data.
Microsoft and Apple know it's important, so you'll find it difficult to set up a new laptop without a user account, but avoid sharing accounts with other people or leaving them unprotected. You can manage user accounts from Accounts in Settings in Windows (via the cog icon on the Start menu), or from Users & Groups in System Preferences (under the Apple menu) on macOS.