Oscar and Florence appear in the 1930, 1920 (as Baumgardner) and 1910 (as Bumgardner) censuses. Oscar appears in the 1900 census as a servant under the name Bumgardner.
The 1880 census shows an Oscar F. Baumgartner 2 as the grandson of Amos Fisher 55 of Franklin Twp., Adams Co., PA. I could not find a Matilda or David that would seem to be the parents of Oscar in any of the censuses. The estate file for Amos may help clear this up.
The 1900 census shows Florence S. Rhodes, born April 1883 in OH, as the daughter of William H. Rhodes, born July 1852 and Annie E., born Feb 1852 in PA. Living with the family is the widowed Sarah, born Nov 1822, mother of William.
Some of these records you can look at for free at labs.familysearch.org and Ancestry.com. For those you cannot see for free I suggest checking with your local libraries to see if they have Ancestry or Heritage Quest.
In the database above you can find William and Annie's death certificates (1924 and 1926 respectively). It has their parents, which interestingly shows his mother as Sarah Cook.