Hi Sam,

Assuming I have the correct family and it isn't a massive coincidence, in 1881 their parents are Bernard and Mary Keegan and their ages :
Sarah Keegan, age 4
Mary Keegan, age 2
Ellen Keegan, age 1
RG11/3726, Folio 8, Page 10
Yet in 1891 Sarah Ann Keegan is 14 years as you would expect, but Ellen who would most likely be Nellie in 1911, is aged only 8 ?
Have you seen this birth for Sarah Ann ?
Birth, Jun qtr 1877
Sarah Ann Keegan
Prescott, Vol 8b, page 650
Pels.