In the censues posted below are John, Swan, and Arthur with their parents in 1900 and 1910. In 1900 John, the oldest, is age 11 and his parents have been married 13 years, leaving little time for a child of this couple born before him (though possible). Only those three boys show up in the 1910 census, at which time Gertrude is 62 and probably not going to have additional children. She was age 41 when John was born.
The 1910 census states Gertrude has had 11 children and 8 are living as of 1910.
If Hans and Gertrude had other children, the child or children would have been born and died between census years.
The five unknown children of Gertrude who survive in 1910 most likely are born to her in her first marriage.
Hans also had been married before.
See the posting history re. this couple in the Sweden Forum (and other forums) for more information about the families in Sweden. Children for both Hans and Gertrude are named in those forums.
Sharon perhaps you would be so kind as to post the URL to the relevant past discussions - or better yet, consolidate the information and post it together in one message here(so that new helpers don't have to click around from post to post).
1900 Ellington, Hancock, Iowa Hans Rapp [Hass Ropp] age 66, born Sep 1833 in Sweden, farmer, married 13 years, year of immigration to USA unknown Jennie 52, born May 1848 in Sweden, married about 1887, married 13 years John 11 Arthur 10 Swan 7
1910 Ellington, Hancock, Iowa Hans Rapp 76 born about 1834 in Sweden to USA 1887, this is his 2nd marriage Gertrude 62 born in Sweden, this is her second marriage, she has had 11 children and 8 are living Arthur Rapp 20 son