Thanks for coming back. Children listed with Leopold and Ottilie on the 1880 census are Oliver (3, so born about 1877), Pauline (1, do b abt 1879).
In the 1900 census (There is no 1890 census for this part of Illinois. Most of the 1890 census for all states was burned in a huge fire.), the children listed are Henry (b abt 1885), William (b abt 1887), Emil (b abt 1890), and Ernst (b abt 1893). There may have been others between Pauline and Henry, but there is no way to tell for sure just based on what is available on the internet that can be checked. There were a lot of Erdmans in Henry County at the time.
The info I have lists the siblings as:
Pauline A. 1875
Minnie t. 1884
Martha M. 1888
Edna M. 1891
Edith M. 1893
Fred E. !895