The technology to run school buses on battery power has just recently become viable, and the Democratic presidential candidates are talking it up. After all, school buses mostly run the same fairly short routes day after day, so a 250-mile range works for most school districts. They're quieter than diesel buses and also greener, even when the power to charge their batteries comes from coal.
The bad news is that we have A LOT of school buses in America (nearly half a million), so replacing the whole fleet would be very expensive. Three presidential candidates (Kamala Harris, Bernie Sanders, and Cory Booker) have all co-sponsored a bill that would provide $1 billion a year to get the process going. That's sort of a drop in the bucket, though, since replacing the whole fleet would cost more than $35 billion.
Bernie has made this part of his $16 trillion "green new deal" plan for the whole economy, which estimates that it would cost $407 billion to convert our whole transit system to clean power. That sounds like a fantasy to me, but given that a fair percentage of buses are replaced every year anyway, there isn't any reason not to get started.