Is Amos really their son?  Assuming Amos is just a few years older than Elizabeth, this is an extraordinary span of fecundity for Deborah.  Or, if Amos is actually "Son A," as the census suggests, then Elizabeth must be Amos's second (or third) wife.

1.  Census Index:  U.S. Selected Counties, 1790 (Broderbund CD-311):  not found, as would be expected if they didn't marry until 1791.

2a.  Census Index:  U.S. Selected Counties, 1800 (Broderbund CD-312).  Please see my WARNING regarding use of this database (the numerical data have the genders switched).

1800

Ely, Amos

PA

Bucks Co.

p. 274

10100-2011000

2b.  1800 Census Images (online at Ancestry.com; Image #37 of 55; extracted by Diana Gale Matthiesen):

1800

PA

Bucks Co.

Solebury Twp.

p. 274

Amos Ely

20110-10100-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
2 males	9 or under	1790-1800	= George = Son A
1 male	16-25	1774-1784	= ?
1 male	26-44	1755-1774	= Amos (b. 1769)
1 female	9 or under	1790-1800	= Daughter A
1 female	16-25	1774-1784	=
0 female	26-44	1755-1774	= Deborah (b. 1769)

The male age 16-25 is too old to be Amos's son.  Is he hired help?  A younger brother?  And is Deborah fibbing about her age already?  Or are we mistaken with regard to her birthdate?  Or is this census-taker error?

3.  1810 Census Images (online at Ancestry.com; Image #2 of 7; extracted by Diana Gale Matthiesen):

1810

PA

Bucks Co.

Solebury Twp.

p. 65B/938

Amos Ely

12101-02001-00

These data indicate:

No. & Sex	Age Class	Therefore Born	Individuals Inferred
1 male	9 or under	1800-1810	= Son B
2 males	10-15	1794-1800	= George = Son A
1 male	16-25	1784-1794	= ?
0 male	26-44	1765-1784	= Amos (b. 1769)
1 male	45 or over	in or bef. 1765	=
2 females	10-15	1794-1800	= Daughter B (b. 1800) = Daughter A
0 female	26-44	1765-1784	= Deborah (b. 1769)
1 female	45 or over	in or bef. 1765	=

Now, both Amos and Deborah are in the wrong age category!  Yet, I don't doubt this is our subjects' household — who else could it be?  Again, we have an unknown male age 16-25, who could only be the same one as in 1800 if he was born in 1794.  The second female age 10-15 could only be their daughter if she was born in 1800.

4.  Census Index:  U.S. Selected Counties, 1820 (Broderbund CD-314):

1820	Ely, Amos	PA	Bucks Co.	Salsbury Twp.	p. 16
1820	Ely, Amos	PA	Bucks Co.	Salsbury Twp.	p. 18

The appearance of two Amoses in 1820 suggests our subjects' "Son A" may have been Amos Jr., in which case, Elizabeth SMITH has to be Amos Jr.'s second  (or third) wife.

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

6.  LDS.  Family Search: Internet Genealogy Service:  AF - Ancestral File (online at FamilySearch.org).