I don't know what the correct answer to this is - Personally, I think it should be non negotiable that all children should be back in school in September - even if that means shutting pubs and using other measures to prevent spread.
I will say that I live in Wales - we are the only country in the UK where mask wearing isn't compulsory (except on public transport) and also the only country in the UK where cases continue to fall - I'll let you make of that what you will, but I think it's probably more to do with the fact that the WAG have been far slower to release lockdown than in the rest of the UK. Shops and restaurants have been open for a while now - with no increase in cases.
There is very little evidence that children (particularly under the age of 11) either suffer from or transmit the virus. Wearing masks even for 15 minutes at a time is very hot and uncomfortable and unless you use surgical disposable masks, they very quickly become damp and unpleasant. Also, if the wearer actually has coronavirus, they will very quickly become saturated with the virus which could mean they make it more likely that the wearer will transmit the virus, not less.
Finally, people who wear masks often think (subconciously) that they don't need to socially distance and are also more likely to touch their faces - thereby increasing transmission of the virus.
So far, there is no scientific study which has shown that wearing masks reduces transmission - probably why the WAG hasn't made them compulsory.
As I said, I don't know the correct answer to this, but I really don't believe that mask wearing is a miracle solution - a proper track and trace system and contact app (Oh wait - what happened to that technology under the Westminster Government?) coupled with immediately self isolating if you/a household contact develops symptoms, plus early testing is far more likely to be effective