Yes, the bus driver who risked his life to save children is a hero. Anyone who risks their own lives or safety for the benefit of others is a hero. Being a hero is about committing selfless acts for other people. Risking your own life is about as selfless as you can get, so he is a hero.
This bus driver is pretty much the definition of hero. He risked his own life, repeatedly, in order to help the children under his care. His selfless act saved the kids. That's being more of a hero than the people we generally think of as heroes in every day life.
The bus driver who risked her life to save the children is a hero. She went back into a burning bus to rescue 20 children, repeatedly risking her own life. The driver ensured the safety of the kids by going back on the bus, and even checking to make sure there were no more kids. She put the kids' lives ahead of her own, a true act of heroism.
Yes, the driver is a hero because that's what heroes do: they protect those in need. He risked his life without thinking. He wanted only to save as many people as possible and we should celebrate him as much as possible. Not everyone would react in such a way. Many would only think of themselves.