Instructions to the enumerator for the 1910 census for that category:
116. Column 10. Number of children born.-This question applies to women who are now married, or who are widowed, or divorced. The answer should give the total number of children that each such woman has had during her lifetime. It should include, therefore, the children by any former marriage as well as by her present marriage. It should not include the children which her present husband may have had by a former wife, even though they are members of her present family. Stillborn children should not be included. If the woman has never had any children, write "0" in this column and also in column 11.
Full instructions: http://usa.ipums.org/usa/voliii/inst1910.shtml
I know in my own family, my 2xg grandmother gave a different answer for total number in 1900 and 1910. By 1910, she was elderly, and I have heard that her memory was failing. Today, she would probably have been diagnosed with Alzheimer's. Another 2xg grandmother was living at the 1900 census and deceased before 1910, but the count for 1900 was far short of the confirmed known children.