Earlier quoted context omitted.
If masks don't prevent you from getting infected then why do medical professionals want masks? Everything I've read suggests that masks reduce your risk of infection, and that pairs with the common sense idea that filters in front of your respiratory tract entrance would reduce the risk of foreign particles entering and infecting you.
Simply putting on a mask does a great deal to limit the spread of a virus you already have - you’re not spewing particles all over your environment due to respiration. Simply putting on a mask does very little to keep you from getting sick, because you’re very unlikely to be following proper PPE donning/doffing procedures. Unless you your house set up as a “clean zone” with two rooms between it and the outside world…
In one of the articles linked in this thread there is a study showing mask usage in children is nearly as effective as intervention against flu as vaccines are. I only read the summary of that paper but I don't think the children are working with clean zones or following doffing procedures carefully.
The article does mention that the effectiveness of masks was greater along older children. To me, that connects with what I wrote earlier. The better you are about using your mask, and here I expect mask diligence comes with age, the better a result you will have, but something is still better than nothing.