The former couple, who split in 2003 after five years of marriage, were spotted enjoying some time on the slopes with their daughter Maya, 15, and son, Levon, 12, after they met up at the Sundance Film Festival in Park City, Utah, reported Us magazine.
"They seemed very comfortable. They looked like a normal, happy family. No tension," an onlooker said.
The duo, both 43, also had lunch with their children at the Stein Eriksen Lodge.
Ethan and Uma have both moved on and had other children since their split.
Meanwhile, Uma has an 18-month-old daughter Rosalind with her on/off boyfriend Arpad Busson.