Ole Pedersen Selseng

I am researching Ole Pedersen Selseng (1808-1903) and Ragnild Tostendatter Alme(1812-1884). They lived on Selseng Farm in Sogn. They went to America around 1848, I think, and settled in the the Mt Morris area of Waushara County Wisconsin. My problem is with 2 of the children: Johannes Olsen Selseng supposedly born in 1836 and his sister Ragnild Oldsdatter also born 1836 on the Selseng Farm. I have found the birth record for Ragnild in the archives to support this birth. I don't believe the date of birth for Johannes Olsen Selseng. I have found census reports in Wisconsin for a John Selseng (1870 census) age 33 and in the 1880 census for Wautoma for John Selseng born abt 1831. I have searched the Archives from 1829 to 1836 and can't find a record for him. In the 1900 census there is a John P Selseng born abt 1840. Hopefully someone can help me clear this up.