Officers said the driver of the van, who is also the baby's father, was arrested for fleeing after he caused the crash.
It happened just before noon Friday at the intersection of 6th Avenue and Hathaway Street.
Investigators said the van pulled out in front of another car. The child was ejected when the van ran into a cement pole.
Police said she wasn't properly strapped into her car seat.
Officers arrested the father a short time later down the street. He faces vehicular assault and hit-and-run charges.
No one else was hurt.
The baby remains in serious condition.