There's an outside possibility that Benjamin is our subject's son, but it would have been extraordinary for Mary to have birthed a child at the age of 47.

1.  Marriage Record:

2.  1840 Census Index/Images (online at Ancestry.com, Image #1-2 of 16 — list was roughly alphabetized; extracted by Diana Gale Matthiesen):

1840

PA

Union Co.

Chapman Twp.

Roll 496

pp. 364A-364B

Ln. 4

Arnold George Jr

112 001 - 020 101

0700000

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	4 or under	1835-1840	= George III (b. 1838/9)
1 male	5-9	1830-1835	= Stephen (b. 1834/5)
2 males	10-14	1825-1830	= Son B = Son A
1 male	30-39	1800-1810	= George II (b. 1803)
2 females	5-9	1830-1835	= Barbara (b. 1836/7) = Daughter B
1 female	15-19	1820-1825	= Daughter A
1 female	30-39	1800-1810	= Mary (b. 1809)
7	persons employed in agriculture

3.  1850 Census Every-Name-Index/Images (online at Ancestry.com, Image #19 of 37):  Chapman Twp., Union [now Snyder] Co., PA, Roll M432_831, p. 154A, 129/129, enumerated 9 Dec 1850, official enumeration date 1 Jun 1850 (extracted by Diana Gale Matthiesen):

George Arnold	47	M		Carpenter	400	Penna
Mary Arnold	41	F				"
Stephen Arnold	15	M				"
Barbara Arnold	13	F				"
George Arnold	11	M				"
Daniel Arnold	6	M				"
Fianna Arnold	1	F				"
Minerva Arnold	7/12	F				"

4.  1860 Census Every-Name-Index/Images (online at Ancestry.com, Image #11 of 45):  Chapman P.O., Chapman Twp., Snyder Co., PA, Roll M653_1182, p. 377, PN 85, 595/619, enumerated 26 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

George Arnold	58	M		Farmer	200	500	Pennsylvania
Mary      "	52	F					"
Stephen   "	23	M		Carpenter			"
Calvin    "	21	M		Do			"
Daniel    "	15	M					"
Fianna    "	11	F					"
Minerva   "	9	F					"
Benjamin  "	5	M					"
Catharine Stroub	3	F					"
Elizabeth Arnold	66	F					"	Idiotic
Eliza Buff	32	F		Servant			"

Catharine STROUB appears to be the daughter of Jonathan France STRAUB and his first wife, Catharine, who died in 1858.  Jonathan has remarried by 1860, so one wonders why little Catharine is living here and not with him.  Is Mary perhaps little Catharine's aunt?  Although Elizabeth's age is off a few years, she is almost certainly George's sister. 

5.  1870 Census Every-Name-Index/Images (online at Ancestry.com, Image #2 of 26):  McKees ½ [Half] Falls P.O., Chapman Twp., Snyder Co., PA, Roll M593_1451, p. 36B, PN 2, 10/10, enumerated 5 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):

Arnold Daniel	28	M	W	Farmer	1000	500	Pa
______ Catharine	26	F	W	Keeping house			"
______ Mary	5	F	W				"
______ George	5/12	M	W				"	Jan
______ Elizabeth	70	F	W	Keeping house			"
______ Mary	53	F	W	"      "			"
______ Minerva	20	F	W				"
______ Samuel	15	M	W	at home			"

Elizabeth's age is now correct, but Widow Mary is telling a whopper of a fib about hers.  Is the Samuel here the Benjamin in 1860?

6.  George W. Wagenseller.  1904.  Tombstone Inscriptions of Snyder County, Penna.  Wagenseller Publ., Middleburgh, PA (facsimile hard copies available from HigginsonBooks.com; online at the Snyder County PAGenWeb site):

p. 83	CHAPMAN TOWNSHIP... GRUBB'S CHURCH CEMETERY... Arnold, George, b Aug 9, 1773; d Mar 11, 1848, aged 74 y 7 m 2 d. Arnold, Maria, w of George, b Feb 7, 1775; d May 13, 1857, aged 84 y 3 m 16 d.
p. 84	Arnold, George, b May 3, 1803; d Dec 2, 1865, aged 62 y 6 m 29 d. Arnold, Mary, w of George, b May 3, 1809; d Apr 12, 1880, aged 70 y 11 m 9 d... Arnold, Elizabeth, dau of George and Elizabeth, b. Feb 24, 1799; d Apr 4, 1878, aged 79 y 1 m 10 d.

Also on p. 83, before the entries for Grubb's Cemetery, are the listings for Kramer's Cemetery.  An apparent mis-reading of this page has led some secondary sources to mistakenly show our subjects buried in Kramer's Cemetery.

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