I have the replacement birth certificate and it shows Isaac Roberts b 1855 Bagillt son of William Roberts collier and Mary Leighton
Also William Roberts collier son of John Roberts collier married 1853 to Mary Leighton dau of William Leighton collier both full age and of Bagillt
witnesses - Enoch Leighton (Mary's older brother - see below) and Margaret Roberts (possibly William's sister?)
Looking at the GRO births index there are 3 other possible children Sarah Roberts b 1854, Sarah b 1857 and Joseph b 1861. There was also a William b 1861 but I found a baptism for Joseph in the Bagillt baptisms booklet son of William Roberts collier and Mary Roberts of Union Row, Bagillt so the Joseph belongs to William/Mary. No baptisms for the other children at Bagillt.
Roberts/Leighton births after 1861 on the index seem to belong to John Roberts m Ann Leighton - Ann I think was Mary Leighton's sister but the John Roberts was from Caerwys not Bagillt but could still be related to William Roberts.
The last Roberts/Leighton birth I can find for William and Mary was in 1861 and I can't find them in 1871 so they could have moved or one or both parents died. I'm struggling to find what happened to the second Sarah Roberts b 1857 and the only possible Joseph Roberts b abt 1861 was in the workhouse in 1871.
Re the Leightons
Fortunately there was only one William Leighton collier in Bagillt in 1841
Pentre Bach
William Leighton 35 collier
Judith 35
Jane 20
Mary 15
Elias 15
Enoch 14
Mary 8
Ann 6
Wm 3
Emas 2
Unfortunately there seems to be 2 Marys! Looking at the original they both look like "Mary" one isn't a Margt. There is a bit of a gap in the ages between Enoch and the second Mary so I wondered if William had remarried and that's why there were 2 Marys? Perhaps there might be baptisms for the children to check for parents names?
In 1851
Willam Leighton 51 collier
Judy wife 47
Mary 18
Anne 16
William 13
Joseph 7
all born Bagillt.
Carole