Family #118 in the 1798 Grimm census.
Family #191 in the 1834 Grimm census.
Anna Christina Bauer was born in 1778 in Scherbakovka, Saratov, Russia.  A review of the 1767 Scherbakovka census shows only one Bauer family resided in the village: Melchior and Anna Elisabeth Bauer, who were 60 and 54, respectively.  Nine years later, Anna Elisabeth Bauer would have been 63 and too old to have a child. But the couple could have been Anna Christina's grandparents.
Melchior and Anna Elisabeth had only one child documented with them in the 1767 census, Georg Friedrich Bauer, and he was most likely Anna Christina's father. At 14 years of age in 1767, he would have been 23 in 1778 and probably married, perhaps for 5 or 6 years already. Anna Christina may not have been their oldest child, as the Volga German immigrants tended to marry young and immediately start their families.
In the 1798 Scherbakovka census, Georg Friedrich Bauer was 46 years old, married to Anna Ott.  The oldest child living in the household was daughter Anna Barbara, age 24; next oldest was son Johann Ludwig, age 18. Anna Christina would have been about 20 years old that year and would have easily fit in between those siblings, based on her age.
As we know from the 1798 Grimm census, Anna Christina Bauer was born in Shcherbakovka but was married by that year to Johann Peter Erdmann. The couple lived in the Erdmann household in Grimm, but had no children.
1798 Grimm Census 
By 1834, it appears that Anna Christina had passed away and her widowed husband remarried to a woman named Eva Christina.
1834 Grimm Census 
Anna Christina was one of two Christinas who were married to Johann Peter Erdmann. Each has a different first name and the same middle name; Anna Christina was about the same age as her husband, but Eva Christina was about three years older that Johann Peter.
There are large gaps between the ages of the Erdmann children in the 1834 census:
One reason for the gaps might be because there were girls born after 1798 who married and lived in different households by 1834. The largest gaps are between the 32 year old and the 25 years old, 7 years, and between the 25 year old and the 17 year old, 8 years. The last three children were born with only 2-3 years between each child.
Another reason for the gaps could be the death of a spouse, typically the mother, if all the children have the same last name. We know Johann Peter Erdmann's first wife died at some point before 1834 because the name of his wife in the 1834 census is different from his wife in the 1798 census. Typically when a mother passes away and children are born to the second wife, a notation is made in the far right column of the census, as in by first wife and by second wife. There is no notation that any of the children have different mothers. That may be the best argument for all the children in the 1834 census listing having the same mother.
Those two large gaps are bothersome, though. Let's say there were two separate mothers involved. Why would the family not mention this to the census taker? Or, if they did tell the census taker, why would he or she not make a note of it? The only answer that makes any sense is because that fact was no longer important. Why would it no longer be important? Perhaps because the only living children who had a different mother were already married with families of their own. Perhaps because the first wife passed away so long ago, who their biological mother was seemed not to be important. The children would have never known their birth mother.
The answer that makes the most sense to this genealogist -- who is also a descendant of Johann Peter Erdmann -- is that all of Anna Christina's children were grown, married, and perhaps some of them living in other households. Only the younger children belonged to second wife Eva Christina, and there is no question about who their mother was. This means the two oldest children, Johann Adam and Johann Friedrich, belonged to Anna Christina. The remaining children, all under the age of 18, belonged to Eva Christina.
For the time being, I have listed Anna Christina as the mother of Johann Adam and Johann Friedrich. If this proves to not be true, and she has more than two children, I will the profiles accordingly.
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