KIMA TV reports that the driver, Jeff Blackburn, was on his route when he saw a woman jogging with her baby in a stroller. She had stopped at the top of a hill, turned the stroller sideways (to stop exactly this kind of thing happening), but the stroller turned started rolling down the hill towards a busy intersection.
Blackburn sped up honking his horn to stop traffic. Then he used his truck to block the intersection and ran after the baby. He and another woman got to the baby just after he went through the intersection and hit the curb.
Thanks to the driver, the baby is fine.