It has nothing to do with emissions. Its a tax to raise money.
I could have a 20 year old car spewing out 100 x more crap than a new car but as long as I pay mayor khant 12.50p. He will invite me in, no questions.
If he said £100 a day for that vehicle then I would agree its for the right reasons.
As for kids and breathing issues, as a poster highlighted the buggy 2 ft from the ground sucking on an exhaust is a lot different to the silver Cross style of yesteryear.
Maybe parents and convenience need to be looked at to start to change the effect on kids.