It would be interesting to see if there are tax rolls or deed records that establish when Abraham Clemmens moved to Reading. I suspect that Elizabeth was the eldest child and that she was married when very young to Joseph Fuchs/Fox. It wasn't unheard of for a girl to marry on or near her 12th birthday. I did the math to see what Christina Clemmons' fertility cycle looked like. Below are the intervals between the births of the children for whom we have records. If we use the average of 2 years 3 months to calculate Elizabeth's possible birthday, we get abt April 1777. The known marriage date would put her just past her 13th birthday...young, but not impossible. If her birth were more toward the longer interval, it would make her a little older. If there were stillbirths or infant deaths between Elizabeth and Margaret, that would push her age at marriage even higher.
9 Jul 1779 9 Oct 17812 years 3 months 6 Feb 17842 years 3 months28 days 1 Oct 17862 years 7 months25 days 23 Oct 17882 years--22 days 4 Feb 17912 years 3 months12 days 30 Apr 17932 years 2 months26 days
The 1784 tax list showing the 5 individuals in Abraham's household could be Abraham and Christina with daughters Elizabeth, Margaret and Christina. Depending on when the tax list was compiled, Maria Esther who was born in February 1784, may not have been born.
I found the following in a Google Books search, which suggests at least the possibility that Abraham may have lived elsewhere in 1772. Fisher, Charles A ., Snyder County Pioneers [Pennsylvania], Genealogical Publishing Company, 2001, p. 17, Google Books. "Abraham Clemens (also Clemmens, Clemmence, Clemance, Clements, Clemmons, etc.) was assessed in Penn Twp. For the first time in 1772, but it seems that his name did not appear again. Because there was no distinction made in the earlier lists between resident and non-resident landowners, the compiler is not sure that this man ever lived in the county. In 1799, an Abraham Clemens, carpenter, lived in the city of Reading, and his name continued there for some years. Edward, Michael and Peter, who lived in the county (Snyder) were possibly relatives of his. An Abraham Clement served with the New Levies, and also in the 9th Pennsylvania Regiment, Continental Line."
Trinity Lutheran Church was founded in 1751, so if they were in Reading all along, the children's births should be recorded there. If they, like other frontier churches, did not have a regular minister, it's possible that they had to wait for a traveling minister to make his circuit and do the christenings. Do we know if the records for Trinity Lutheran extend before 1779? I notice that daughter Christina's 1782 baptism was at another Reading church, Schwartzwald Reformed. This hints that the Clemmens weren't regularly settled in a church until after this date.