Based on the 1900 census and on her biographical sketch, Catharine had only the above five children with only three surviving, which means these two children are attributed to them incorrectly, which also solves the problem that Curtis and Flora were born only a month apart.
.  Flora J. STROUP, b. 6 Aug 1874; d. 21 Feb 1875
.  (Child) STROUP, b. Aug 1881; d. 5 Sep 1881

1.  Marriage Record:

2.  1870 Census Every-Name-Index/Images (online at Ancestry.com, Image #13 of 16):  Jonestown P.O., Davidson Twp., Sullivan Co., PA, Roll M593_1453, p. 41A, PN 13, 82/86, enumrated 16 Jun 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Taylor James	60	M	W	Farmer	10000	2500	Pa
______ Adelia	60	F	W	Keeping house			Pa
______ Alfred	35	M	W	Works on Farm	1200	400	Pa
______ Catharine	33	F	W				Pa
______ Sarah M	2	F	W				Pa
______ Laura	6	F	W				Pa
Stroup James	26	M	W	Work on Farm			Pa

Either this census record is grossly in error or the 1866 marriage date given for our subjects in Catharine's bio is in error because James and Catharine certainly do not appear married here.  What does appear to be the case is that Sarah M. is Catharine's illegitimate daughter and that she's the Margaret S. in the 1880 census, having been adopted by James.

3.  1880 Census Every-Name-Index/Images (online at Ancestry.com, Image #19 of 30):  Davidson Twp., Sullivan Co., PA, Roll T9_1195, p. 615C, PN 19, SD 5, ED 232, enumerated 17 Jun 1880, official enumeration date 1 Jun 1880 (extracted by Diana Gale Matthiesen):¤•

1880:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

8

9

10

13

21

24

25

26

159

159

Stroup James

W

M

37

/

Farmer

Pa

Pa

Pa

______ Cathren

W

F

40

Wife

/

Keeping House

Pa

Pa

Pa

______ Marget S

W

M

12

Dau

/

/

Pa

Pa

Pa

______ Curtis D

W

M

5

Son

/

Pa

Pa

Pa

______ Taylor M

W

M

4

Son

/

Pa

Pa

Pa

Willson George

W

M

21

Boarder

/

Laborer

Pa

Pa

Pa

Catharine is fibbing about her age.  Margret S. here appears to be the Sarah M. in the 1870 census and has to be the "Maggie" in Catharine's bio (see below).  Listed next to Catharine's uncle, Robert TAYLOR (æ 76, b. PA, wife Mary).

4 .  1890 Census:  the 1890 Census Population Schedules were destroyed.

5.  1900 Census Every-Name-Index/Images (online at Ancestry.com, Image #26 of 35):  Davidson Twp., Sullivan Co., PA, Roll T623_1487, p. 63B, SN 13, SD 5, ED 64, enumerated 23 Jun 1900, official enumeration date 1 Jun 1900 (extracted by Diana Gale Matthiesen):¤•

1900:  for an explanation of the column headings, please see What the Numbers in the Federal Census Mean (missing columns contained no data).

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

19

20

22

23

24

25

26

27

28

246

255

Stroup Catharine

Head

W

M

Oct 1837

62

Wd

5

3

Pa

Pa

Pa

Farmer

0

Y

Y

Y

O

F

F

57

______ Curtis D

Son

W

M

Sep 1874

25

M

5

Pa

Pa

Pa

Farm Laborer

1

Y

Y

Y

R

F

______ Laura

Wife

W

F

May 1870

30

M

5

4

4

Pa

Pa

Pa

Y

Y

Y

______ James L

Son

W

M

Nov 1895

4

S

Pa

Pa

Pa

______ Harry D

Son

W

M

Dec 1897

2

S

Pa

Pa

Pa

______ Franklin D

Son

W

M

Jun 1898

1

S

Pa

Pa

Pa

______ Emery

Son

W

M

Nov 1899

7/12

S

Pa

Pa

Pa

Can't find daughter, Maggie, in the 1900 census (there are five George CROWLEY's in PA, but none are married; and, there are six Maggie CROWLEY's in PA, but the only married one has husband Timothy).

6.  George Streby.  1903.  History of Sullivan County, Pennsylvania.  Sullivan Gazette, Printer, Dushore, PA (information extracted and online at the Sullivan County PAGenWeb site).

MRS. CATHARINE H. STROUP She is a daughter of James Taylor, of Davidson Township, and a granddaughter of Robert Taylor, one of the first settlers of Shrewsbury Township.  Her mother was Delia Edkin whose family were among the early settlers of Shrewsbury Township.  She was married in 1866 to James F. Stroup, who died about 15 years ago.  To them have been born five children:  Maggie, married George Crowley; Johanna who died at the age of six months; Taylor; Delia who died in 1882, and Curtis who married Laura Brink, of Eaglesmere in 1895 and who lives on the homestead and conducts the farm.

Either the 1870 census is wrong or the 1866 marriage is wrong and is intended to cover up the fact that Maggie was Catharine's illegitimate child, born before she married James STROUP.  If James legally adopted Maggie, there should be court proceedings to that effect.