— born in MO:
.  James Monroe CHRISMAN, b. 23 Feb 1834  {1850: 17, MO; 1870: 35, MO; 1880: 46, MO}
.  Rebecca CHRISMAN, b. 1835/6  {1850: 14, MO}
.  Preston CHRISMAN, b. 1838/9 {1850: 11, MO}
There's an eight to nine year gap here.
.  Samuel CHRISMAN, b. 29 Jul 1848 {1850: 2, MO; 1860: 10, MO}; d. Mar 1897, Lafayette Co., MO; m. Mary J. HALLOWAY/HOLLOWAY

The gap between births suggests Cynthia may be Gabriel's second wife and that the prior children are those of the first wife.  The marriage records would really help here.

1a.  Jordan R. Dodd, ed.  1993.  KY, NC, TN, VA, WV Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-229):  not found (parents or children).

1b.  Jordan R. Dodd, ed.  1993.  Missouri Marriages:  Early to 1850.  Liahona Research, Orem, UT (Broderbund CD-227):

2.  1830

3.  1840

4a.  Census Index:  U.S. Selected Counties, 1850 (Broderbund CD-317):  not found (Cynthia was overlooked).

4b.  1850 Census Images (online at Ancestry.com; Image #60 of 264):  Washington Twp., Jackson Co., MO, p. 256B, enumerated 19 Aug 1850 (extracted by Diana Gale Matthiesen):

Chrisman Cynthia	44	F	Farming	2000	Va
"     Monroe	17	M	Do		Mo
"     Rebecca	14	F			"
"     Preston	11	M			"
"     Samuel	2	M			"
Parsons Susanna	65	F			NC

As widows are prone to do, Cynthia appears to be fibbing about her age, though a birth in 1805/6 actually makes more sense than one in 1797 because the latter date makes her older than her husband and too close to her mother in age — and Susanna is almost certainly Cynthia's mother.  Living next door to Cynthia's daughter, Elizabeth, wife of John POE, who is living next door to widow Phoebe (FLANNERY) CHRISMAN, second wife of Abraham CHRISMAN, Gabriel's brother, who died in California in 1850.

5.  WorldConnect / Ancestry World Trees (online at RootsWeb.com/Ancestry.com).