I'm so confused about virus and malware on Macs

Those companies were lying to you. You do not need anything unless there is a specific problem, in which case there's usually free or low cost software to address a specific issue. Get rid of any cleaning or virus scanning software. It may be hard to do this because often those thing are almost malware unto themselves.

If your children are using your computer you need to set up separate accounts for them with restricted access to features such as installing software. They are probably not old enough to realize there are many scam web sites out there and they will believe it when they are told their computer has a virus and they need to download something.

Have a look at:

Malwarebytes - https://www.malwarebytes.com/pricing/ - There are different versions available depending upon what features you want. For a single removal without ongoing monitoring you can probably use the free version (make sure you select this version as most companies will understandably try to guide you to pay versions of things).

You do not need those programs and the company you contacted scammed you. While there are no viruses that affect a Mac if you're not careful you can get adware/malware. Mac OS has it's own protections against malware, including needing to authenticate to install programs. But sometimes the malware will hide inside applications you do want and you won't know it's there until you've installed it.

The most effective defense against malware is Malwarebytes. Malwarebytes was developed by one of our own colleagues here in ASC and is about the most proven anti-malware software for Mac. There is a free version you can download.

For a more in-depth explanation see:

Effective defenses against malware and other threats