Illegitimacy in the 1870s

In tracking my grandfather's birth cert for a dual passport application, I have done well. I found my great grandfather's name FRANK (not Francis) Walsh and his wife, Margaret Farraher (or sometimes Farriher) and have myself visited their cottage in Shrule many times (listed as Brodella, Boherbee or Brodullah or Shrule--if someone can explain that to me I'd be grateful) but here's the thing: Frank was born in 1834, married Margaret in 1861 and dutifully (according to their baptismal records) produced:

Peter in 1863

Mary in 1866

Cath in 1868

John in 1873

Winny in 1875 

Margaret in 1876

Pat Frank (a locally famous musician) in 1877

and the one I am searching for, Michael J Walsh in 1882. (I can't find a birth cert or baptismal record for him, naturally, and that the one I need! Any help would be very welcome before I have to cough up a fortune to someone over there to dig it up.)

But, here's the rub--in 1871, when old Frank seems to have given Margaret a break for breeding, another child named Mary was baptised at Shrule, born of Margaret Henehan (!) and FRANK (not Francis) Walsh. Shrule is not a very big place and Frank (not the saintly Francis) not a usual name. Was this a bit of hanky-panky on Frank's part and would the Church have baptised an illegitimate child born of the union between an unmarried woman and a married man? (It may be why Frank (died 1913) is buried in Shrule's St. Joe's cemetery with only his name on the tombstone?

Does anyone know about this sort of thing? 

Thanks in advance...kittwalsh@yahoo.com