Instead of punishing the middle class by slapping ulez on them, it would be far more effective and fair for the london mayor to offer free school buses like they do in some parts of America.
I'm not sure the middle classes are likely to be hit by ULEZ anyway - it hits vehicles older than a certain age, primarily - not many of those Chelsea Tractors are likely to fall foul of it. While I agree with ULEZ, I will admit it's quite regressive - the people with old/polluting vehicles are, in many cases, those least able to afford anything better and/or the charge. Public transport should be much better, but that's way beyond the scope of something the mayor can quickly impact.
We need the need to follow Paris's lead and tax by weight - damage to roads follows a 4th power law, so very from a dumb immediate economic POV this makes sense.
Add to that the production of newer ones just negated the effeciency gain.
Children under 16 already get free travel on buses and trams in London, though they have to pay discounted fares on the tube and they'll need a photocard if they are 11 or over.
I'm aware of that having owned one and journeyed by bus to school every day. I also see vast amounts of traffic near schools during term times. So from personal observations and experience that's not nearly enough.
Ummmm under sixteens have had free bus and tram travel in London for years. Or do you not want them to interact with members of the public and live in a sanitised bubble consisting solely of you and your nanny?
School children already have free bus travel in London.