Here are all the Mundall and variant births [before civil registration] from the Derry genealogy site [closed presently] from the CSI index at
www.irishgenealogy.ieLooks like your family is amongst these births.
MUNDALE HESTER 1817
MUNNELL ESTHER 1823
MUNNEL ELIZA 1824
MUNDALE ANNE 1825
MUNDLE JOHN 1826
MUNNELL THOMAS 1828
MUNNEL JAMES 1828
MUNDALL THOMAS 1829
MUNDALE MARTHA 1830
MUNNELL JANE 1831
MUNNELL JOHN 1833
MUNDALL WILLIAM 1833
MUNNELL WILLIAM 1835
MUNDALL ELIZA 1838
MUNDALL THOS JAS 1841
MUNDAL WILLIAM 1844
MUNDLE SAMUEL 1845
MUNDALL RACHEL 1847
MUNDALL MARIA 1854
I would hazard a guess that your family were using St Columb's
Cathedral [Templemore parish Church] for their baptisms.
Although Derry genealogy centre is closed at the moment their
records will becoming online soon at the following site
http://ifhf.brsgenealogy.com/Keep an eye out for updates but it will cost you 5 euros for each
birth/baptism, which is quite expensive.