1a.  Jordan R. Dodd.  1997.  Virginia Marriages to 1800.  Liahona Research, Orem, UT (online at Ancestry.com).

Keen, Moses married Siers, Rhoda on 10 Jun 1800 in Monroe County, Virginia

Mann, Moses married Siers, Rhoda on 10 Jun 1800 in Monroe County, Virginia

All I can guess is that the transcriber was uncertain of Moses's surname, so gave it both ways, though how "Keen" and "Mann" could look like one another is a mystery to me.  And if that weren't mystery enough...

1b.  Jordan R. Dodd, et al.  19xx.  Early American Marriages: Virginia to 1850.  Precision Indexing Publishers, Bountiful, UT (online at Ancestry.com):

Moses

Keen

Rhoda

Simms

10 June 1802

Monroe Co.

1c.  Jordan R. Dodd, ed.  1993.  Virginia Marriages: Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):

Keen, Moses	Siers, Rhoda	Jun 10, 1800	Monroe Co.
Keen, Moses	Simms, Rhoda	Jun 10, 1802	Monroe Co.

1d.  Marriage Bonds by Bride, 1799-1819 - Monroe Co. WV (online in the Archives of the Monroe County WVGenWeb site):

Keen, Moses

Sim, Rhoda

3/12/1801

2.  Census Index:  U.S. Selected Counties, 1810 (Broderbund CD-313):  the 1810 VA/WV census was lost.

3.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):  can't find.  Based on the children's birthplaces, he should still be in VA/WV.

4.  Census Index:  U.S. Selected Counties, 1830 (Broderbund CD-315):  can't find.  Based on the children's birthplaces, he should still be in VA/WV.

5a.  Census Index:  U.S. Selected Counties, 1840 (Broderbund CD-316):

1840	Kearn, Moses	AR	Conway Co.	Petit Jean Twp.	p. 60
1841	Kearn, Moses	AR	Conway Co.	Petit Jean Twp.

6b.  Conway County, AR, 1840 Federal Census (online at the Conway County ARGenWeb site; transcribed by Sondra Johnson):

1840

AR

Conway Co.

Pg. 60

Ln. 9

Kean Moses

110 000 001 - 010 000 000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	4 or under	1835-1840	= Jasper (b. 1837/8)
1 male	5-9	1830-1835	= John (b. 1830)
1 male	60-69	1770-1780	= Moses (b. 1770)
1 female	5-9	1830-1835	= Daughter A

Rhoda was too old to have children much past 1825-30.  Therefore, while John might have been Rhoda's child, Jasper and Daughter A certainly were not.  This fact suggests there was a second wife, after Rhoda, who has died before 1840.  It is also possible, but I believe much less likely, that these are his orphaned grandchildren.  My reasoning is that saddling a grandfather who is just shy of 70 years old with three children under 10 years of age is much less likely than that the orphans would be taken in by one of their aunts or uncles or even some younger couple in the community.  The most obvious and most compeling reason I can think of for three small children to be living with an elderly man would be that they were his children.  And my guess is that Moses, with three young children needing care, didn't remain a widower for long.  That is, that Wife-2 died not much before the 1840 Census (perhaps in 1838, giving birth to Jasper) and that Moses remarried shortly after the census.

6.  1850 Census Index/Microfilm (online at GenealogyLibrary.com):  Griffin Township, Conway Co., AR, p. 262, 489/489, enumerated 8 Dec 1850 (extracted by Diana Gale Matthiesen):

Moses Kean	80	M	stone mason		Virginia
Mary   "	40	F			"
John   "	20	M			"
Jasper "	12	M			"

Because Mary was not in the household in 1840, she it is unlikely that she is an unmarried daughter.  It is most likely that Mary is a third wife of Moses, and there are any number of reasons why she might not have any children of her own, either with Moses or a previous husband, if there was one.

7.  Ancestry World Trees (online at Ancestry.com).  Says the two younger males in the 1850 Census are William Johnson SIERS and William Jasper SIERS.

8. Greenbrier County, West Virginia. Deed Book 2, 1798-1803, p. 126.  LDS FHL Film No. 0593545.  Quoting Anderson:

p. 126

16 May 1798

John Siers sold livestock and personal property to James Graham in Greenbrier co... Rhoda Siers witness...

Rhoda had to be 21 to witness a deed, so she must have been born in or bef. 1777.  It seems odd to me that a man would have had his daughter witness a deed, if indeed she is his daughter.