Lost relative - Kolbjørn Kristiansen

Good Afternoon, I am trying to track my late grandfather's half-brother. I found Kolbjørn on the 1900 census with his mother, Tora Kristianson. I am not sure where his father, Ole was living at that time. Kolbjorn was born in 1900. When Ole, Tora and their daughter (born in 1902) left for America in 1904, Kolbjorn was not with them. I was wondering if there is a way to find out what happened to Kolbjorn? Thanks, Dawn Wisconsin