Said to have had this child, but if so, he died before the 1860 census:
.  Oscar David DRESSLER, b. ca. 1857

Hannah either divorced Joel and took the children with her, or she died, and her kin took the children in, because they do not show up in the 1870 census with their re-married father.  Either that or the Joel DRESSLER who married Hannah is not the same Joel DRESSLER who married Kate STROUP, which appears to me to be a distinct possibility.

1.  Marriage Record:

2.  1860 Census Images (online at Genealogy.com; Image #3 of 39):  Thompsontown P.O., Delaware Twp., Juniata Co., PA, p. 499, PN 47, 330/1, enumerated 19 Jun 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):¤

Joel Dressler	30	M		Lab. P.R.R.		100	Penna
Hannah Dressler	29	F					"
Nancy	4	F					"
John	2	M					"
Henry	6/12	M					"

3.  1870 Census Images (online at Ancestry.com; Image #8 of 23):  Mahontengo P.O., Susquehanna Twp., Juniata Co., PA, p. 465B, PN 8, 53/53, enumerated 13 Aug 1870, official enumeration date 1 Jun 1870 (extracted by Diana Gale Matthiesen):¤•

Dressler Joel	41	M	W	Farmer	2000	600	Pa
________ Kate	30	F	W				Pa
________ Alfred	16	M	W	L $			Pa
________ Sarah	14	F	W				Pa
________ Daniel	12	M	W				Pa
________ Jerimiah	10	M	W				Pa
________ Agnus	1	F	W				Pa

The three eldest children are Kate's by her first marriage, to Mr. ZELLERS — by the way, we know that Alfred used the surname ZELLERS, not DRESSLER.  If Jeremiah is 10, as it says here, then he has to be a son of Mr. ZELLERS.  If he is 3 years old, as indicated by the 1880 census, then he is Joel's biological son, not his adopted son.  Living three doors from Michael & Eva Maria STROUP. 

4.  1880 United States Census and National Index (LDS Family History Resource File: CD-ROM Library):¤•

Census Place: Susquehanna, Juniata, Pennsylvania
Source: FHL Film 1255137; NARA Film T9-1137; Pg 360A
	Relation	Sex	Marr	Race	Age	Birthplace	Occupation	Fa	Mo
Joel DRESSLER	Self	M	M	W	52	PA	Farmer	PA	PA
Catherine DRESSLER	Wife	F	M	W	46	PA	Keeping House	PA	PA
Jeremiah E. DRESSLER	Son	M	S	W	13	PA	Works On Farm	PA	PA
Jasana A. DRESSLER	Dau	F	S	W	11	PA	At Home	PA	PA
Joel T. DRESSLER	Son	M	S	W	9	PA		PA	PA
Louisa C. DRESSLER	Dau	F	S	W	7	PA		PA	PA
Amelia U. DRESSLER	Dau	F	S	W	5	PA		PA	PA

If Jeremiah really is 13, then he was 3, not 10, in 1870, making him Joel's son, not Mr. ZELLERS's.  The fact that Joel calls him "son" is not proof he's Joel's biological son, because I know of many cases where adopted children are not so indicated in the census.  Living next door to John & Susanna CUPP, who are next door to Michael & Eva Maria STROUP.