Have you heard stories about your grandmother having had babies that passed away but can't find any records of them? When piecing together members of a family a great way to find children that may have been forgotten or overlooked is to to use the 1910 Federal Census and tombstones. On the 1910 Federal Census line number 10 asks the female/wife how many children she gave birth to and line 11 asks how many are still alive. If in between census years the deceased children could get lost.
By using the 1910 federal census for location you can search local cemeteries. When finding the correct cemetery you may find a stone like this one. This could be a great clue to unknown aunts, uncles, or cousins. Many times these children are buried close to their parents. These children would not have been enumerated on any Federal Census.
If your lucky you might hit the mother load and a lot more information, as on this headstone:
One thing to remember is that in some cemeteries small children are buried in their own section. The reason for this, I suspect, is the lots would probably cost less.