With schools trying to restart the role of children is important.  This report of research from South Korea is interesting in that they have a great testing policy so the data is likely to be better than many other parts of the world.

The conclusion is

Children can carry coronavirus in their noses for up to three weeks, according to a study from South Korea.

But they are not sure how that translates into the models of children spreading the virus, as mild cases have less coughs and sneezes.

https://www.bbc.com/news/health-53946420" rel="noopener noreferrer - https://www.bbc.com/news/health-53946420

I wonder if there is anything out there like a universal virus killing nasal spray ?

I mean if the virus is confined in the nasal passages ,

it should be easy to attack? 

Or not ?, 

I'll handball that to an expert....Doc...

Carbon, this is where I believe in a Neti Pot or Neil Med bottle.  Specially buffered saline solution to flush out the nasal passages.  I began using Neil Med solution that I introduced into my nose via an ear syringe.  (I couldn't get the hang of a Neti Pot, and the Neil Med bottle was too forceful, and backwashed the solution into my ears, causing vertigo, etc.).  I used a technique I saw on YouTube and it worked very well for some persistent allergies I couldn't get rid of any other way last summer, which had caused a bad bronchitis.  I'm sure something like this would not be foolproof, but in the absence of anything foolproof, it would probably help quite a bit, and better than doing nothing.