Sarah's birthdate is almost certainly incorrect, for two reasons:  1) men only very rarely married women older than themselves, and 2) if she was born in 1733, then she would have been 55 years of age when she birthed Abraham, which is biologically impossible.  "1733" was probably someone's misreading of "1738" or, more likely, a typo of "1743."  Getting married at 15 is much less far-fetched than having a baby at 55, or even 50.

Based on early geographic proximity in MD, these are very likely Nathan & Sarah's children, though they do not appear later in Clermont Co., OH:
.  Thomas CORBIN, b. bef. 1774; m. 1790, Harford Co., MD, Nancy TURNER 
.  Delia CORBIN, b. 1774-84; m. 1797, Harford Co., MD, Thomas TURNER 

There is a Margaret CORBIN (b. 1775/6, MD) in the 1850 census of Clermont Co., OH (living with the DOUGHTY family), who, if unmarried rather than a widow, may be "Daughter A." 

1a.  Robert Barnes.  1978/93.  Maryland Marriages, 1778-1800.  Genealogical Publ. Co., Baltimore, MD (Broderbund CD-195).

p. xi	2 BA - St. John's and St. George's Parish; copy made by Harrison, at MHS [Maryland Historical Society].  (Despite the title of the manuscript, the records are chiefly those of St. John's Parish.)
p. 40	Corbin, Nath'l, 16 Oct. 1758, Sarah James 2 BA-217

1b.  LDS.  Family Search: Internet Genealogy Service: International Genealogical Index (IGI).

Abraham CORBIN Birth: 6 Mar 1788, <>, Clermont, Ohio Father: Nathan-Nathaniel CORBIN; Mother: Sarah JAMES Source: [patron submission]

Abraham CORBAN Christening: 26 Aug 1792, Saint James Protestant Episcopal Parish, Baltimore, Baltimore, Maryland Father: Nathan CORBAN; Mother: Sarah Source: Index to the register of births, marriages and deaths in St. James' Parish, Baltimore County.

Nathan CORBIN Birth: 17 Jun 1776, Baltimore, Maryland Father: Nathan-Nathaniel CORBIN; Mother: Sarah JAMES Source: [patron submission]

They could not have been in Ohio as early as 1788 (only explorers and trappers — and Amerinds — were in the Northwest Territory that early, not European settlers), and Abraham's baptism in 1792 proves they were still in Maryland.

2.  Census Index:  Colonial America, 1607-1789 (Broderbund CD-310):  not found. 

3a.  Census Index:  U.S. Selected Counties, 1790 (Broderbund CD-311):  not found.  The Nathan CORBIN in Baltimore Co., MD, is the one who married Susannah ANDERSON and stayed in Maryland. 

3b.  1790 Census Index and Digital Images (online at Ancestry.com):  I searched all of Harford Co., line-by-line, and did not find Nathan CORBIN.

4.  1800 Census Index and Digital Images (online at Ancestry.com; Image #4 of 12; extracted by Diana Gale Matthiesen):¤•

1800

MD

Harford Co.

District 1

Roll 11

p. 7/73

Ln 7

Nathan Corbin

01101-00201-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	10-15	1784-1790	= Abraham (b. 1788)
1 male	16-25	1774-1784	= Nathan Jr (b. 1776)
1 male	45 or over	in or bef. 1755	= Nathan Sr (b. 1738)
2 females	16-25	1774-1784	= Nathan Jr's Wife: Sophia (b. 1777) = Margaret? (b. 1775/6)
1 female	45 or over	in or bef. 1755	= Sarah (b. 1743)

Nathan, Jr., and Sophia are newlyweds.

5a.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313):  not found, but then, the entire 1810 Ohio census was lost (except for Washington Co.).  Some tax lists are substituted on this CD, including ones from Clermont County, but, again, not found.

5b.  Clermont County Ohio — 1810 Tax List Index [link died] (online at the Clermont County OHGenWeb site; contributed by Hope Freeman Carnicle):  no CORBINs on this list.

6.  1820 Census Index and Digital Images (online at Ancestry.com; Image #2 of 12; extracted by Diana Gale Matthiesen):¤•

1820

OH

Clermont Co.

Ohio Twp.

p. 29/56

Ln. 18

Sarah Corbin

000100-00011-0-000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	19-25*	1794-1801	= hired help?
1 female	26-44	1775-1794	= Margaret? (b. 1775/6)
1 female	45 or over	in or bef. 1775	= Sarah
0	persons engaged in [anything]
*In the 1820 Census, the third column is age class 16-18 and the fourth column is age class 16-25; therefore, any individual in column three is duplicated in column four.  By subtracting the number in column three from the number in column four, you can create an age class "19-25."

The male is too young to be Sarah's son.  Listed four lines from son, John CORBIN. 

7.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).