I searched the Irish Family History Foundation's database. It contains 12,000,000 surviving rcds for abt 65% of Irish counties. Rcds B4 1840 are sparse, B4 1800 rare. I only search the 65% which are.
For a marriage of Luke and Mary in 1838 +/- 4 yrs, I found 60 rcds for Mary and 1 M rcd (1842) for Luke (Mulloy) in Co. Cavan. 5 of the Mary rcds were also in 1842. Searching by parish, the common parish was Killinkere. These are LIKELY your ancestors.
Searching in Killinkere parish for the surname Molloy and the Father's name of Luke, I found B rcds for Philip (43, 55, 57), Michael 44, Anne 43, Mary 46, and Luke 51. There appear to have been at least two families headed by a Luke Molloy during this era. For the other children, it appears their B rcds didn't survive, or they were born elsewhere. Will leave these rabbits for you to chase.
Google the Foundation's name to lead you to the database. Register, opt to be notified as rcds are added and browse. Pls post your search results to my genforum msg.