What is Santaif?

"What is santaif?" my six-year-old asked as we drove down the street.
"What is what?" I asked.
"Santaif!"
The other kids all started talking at once.
"What?"
"That's not a word."
"I've never heard that word before."
"What is it?"
"Santaif!" my six-year-old insisted.
"Did you make that up?" I asked.
"No."
"You'll have to spell it," my husband said.
"Where did you see it?" I asked.
"On a train."
Oh.
"Santa Fe!" we chorused.