Google Chrome notification of virus

Chrome (and every other web browser) CANNOT look at your system and find viruses! Web browsers are sandboxed and prevented from looking at anything outside of the code and resources associated with the web browser.

What you have received is an Advertisement. And the Advertisement LIED! Lies, Lies, Lies.

The Ad wants to scare you into clicking on their link, installing their software, calling their phone number, etc... all so they can most likely get money from you. Or worse get you to install something that will harvest all your data for nefarious purposes (none of which are good for you).

Ignore the advertisement. At most clean Chromes browser cache.

Notifications:

Google Chrome Helper (Alerts).app

one notification

The context of your question and the Etrecheck report both suggest that you agreed to have a Google Chrome webpage send you Notifications. You ought to be able to disable them in Google Chrome's Settings or Preferences.

Even though it specifically refers to Safari, the following excerpt from Effective defenses against malware and other threats - Apple Community probably explains what you encountered:

• Beware spontaneously appearing, unsolicited popups demanding immediate action. Think before you click.
  • ...
  • If you encounter a website, popup, text message, email, or phone call alleging your Mac is infested with some ick or that you need to take immediate action lest dire circumstances ensue, it is 100% fraudulent. Ignore it. Read Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams.
  • The same goes for website Notifications — attention-getting banners that appear at the top right corner of your screen. Safari gives you a great degree of control over them: Customize website notifications in Safari on Mac. Most of those Notifications are simply annoying, but some are intended to frighten and deceive you into installing something nefarious.

Investigate Google Chrome's equivalent website notification settings.

When a webpage offers to send you Notifications it's usually best to decline the offer. Most of them are needless and annoying. A Notification by itself can do nothing, nor can the webpage that loads when you click it. All it can do is cause needless concern in an effort to convince you to install something on your Mac and (perhaps) extort money from you to fix it. That's the threat. "Just say no" slams the door on that threat.

Further advice, if you encounter one of these erroneous popup threat pages the first thing I do is:

command-option-escape on a Mac

Select the browser that I was running and hit Force Quit.

On Windows

control-alt-delete, select task manager

find the browser in the last of tasks and end task on it.

Once done hold the shift key when you reopen each web browser that was not running. It will allow you to choose not to open the last page. You want to open the homepage or blank page instead.

This gives you a chance to dump the caches, and start with a clean slate. Granted any of your browsing history during the incident will be gone, but better safe than to accidentally run into that page again.

to post the report here, please see How to use the Add Text Feature When Posting Large Amounts of Text, i.e. an Etrecheck Report

Your youngest might as well learn early that the primary reason for the Internet in general — and Google in particular — is to sell you stuff you don't need. The clearly defined parameters you seek can best be summed up in that undeniable fact of life.

Avoiding advertisements, encompassing a range from enticing to threatening to outrageous lies as BobHarris explained is a nearly impossible task, if for no other reason that Google derives nearly all its revenue from them. There is no "truth in advertising" clause on the Internet. Anyone anywhere around the globe can lie with impunity, and they do so with reckless abandon.

You don't have to play their game; just remain vigilant. Effective defenses against malware and other threats - Apple Community and the links within it is a good place to start. It's family-friendly, and appropriate for all ages.