City Hall has previously said that almost every London school is in an area where air pollution levels exceed World Health Organization limits.
Air pollution was found to have caused the death of schoolgirl Ella Adoo-Kissi-Debra in Lewisham, south-east London, a coroner ruled in December 2020.
Her mother Rosamund, who is holding a vigil on Sunday on the eve of what would have been Ella's 18th birthday, said one measure "won't solve everything".
"Anything that can reduce car use generally, I'm going to be for it," she said.
"I know there will be huge impacts on certain jobs but the health impacts are so detrimental that something has to be done. I don't think there's a choice really."
The RAC said everyone wanted cleaner air but cleaner vehicles were too expensive for most people and such charges would impact carers, tradespeople and night-time economy staff.
Head of roads policy, Nicholas Lyes, said: "Our research suggests fewer than a third of drivers in London expect to switch to an electric vehicle within the next five years and, at the same time, the mayor himself cannot commit to a zero-emission TfL bus fleet until 2037.
"At a time when the basic cost of living for Londoners is soaring, these proposals seem to be poorly timed, so we strongly urge the mayor to think again instead of defaulting to extracting more money from the pockets of London's drivers."
Mr Khan added: "I'm determined that we continue to be doers, not delayers - not only to protect Londoners' health right now, but for the sake of future generations to come."