My bet is that the list of children was mangled by the census taker or by the person providing the information [which may not have been a family member]. Frederick's mother shows that she had 4 children, 3 still living, on both the 1900 and 1910 censuses. Maybe Cleora was the child who died [perhaps even a recent death], and the entry for the family in 1900 got messed up.
I would not merge Frederick and Cleora, but search births and deaths in Kansas or Illinois for evidence of Cleora or siblings. May never find it unfortunately, but you could leave a research note on her profile about the search and the theory.
Just my opinion. Hope that helps!