How can I tell if these startup items on my nephew’s PC are viruses?

You might want to run some additional programs like Malwarebytes and CCleaner. Sometimes uninstalling apps can leave remnants in the startup list that won't let you access the file location anymore. So, a couple of scans could help clear things up.

Try right-clicking on any entry you're unsure about in the Task Manager and select 'Open File Location'. This will show you where the file is stored, which might help you identify if it's safe or not. But generally, a true virus wouldn't disable itself at startup. Just be cautious with anything that seems too unusual.

It's tough to determine just from the filenames whether something is a virus. This is why antivirus tools are essential! Definitely run Windows Defender or another antivirus program to check it out.

A good first step is to use Windows' built-in antivirus software. Just run a full scan and see if it picks up anything suspicious. It's free and can catch most common threats.