Matthias Bergsven family

Mathias Bergsven (b. Feb. 15, 1833 in Illeulland, Faberg, Norway) left Norway, supposedly April of 1883 with his wife, Mari, dau. Annetta. son Martin and another infant, names Olaf Bergsven. They went thru Liverpool and arrived in Pennsylvania May 10, 1883 and headed to Crookston. My question is the infant Olaf. I have been unable to find any birth record of Olaf Bergven. Mathias and Mari had another son, Ole, who died at the farm of Bergsveen, but this Olaf is a mystery. Any suggestions on how I can discover who he is? (They also had another son, Christ Matteson, who had already come to America and settled). Thank you, Dusty