Isaac Fleming Young
The 1850 Utah census shows Isaac Fleming, age 4, born in Missouri, with Lydia Caroline Fleming. Isaac and Lydia would have arrived in Utah in 1847 or 1848 because she was rebaptized in Salt Lake City on 22 October 1848.
FamilySearch shows an Isaac Fleming Young (2SQ5-5YL) as the son of "Caroline L. Hager," and Joseph Young, born 20 November 1850. His birth year does not match with the 4-year-old Isaac, born in Missouri, that appears with Lydia in the 1850 Utah census.