Hi Manus,
I can't add much to what Lisa told you already.
The key question here is 'where did they get married?'
If they got married in a Catholic Church, the non-Catholic would have to give an undertaking that all the children of the marriage would be brought up as Catholic. Although, as far as I know it was not mandatory for a non-Catholic to convert to Catholicism, it appears that most of them did.
If they got married in a non-Catholic Church there was no declaration and no need to convert.
Dara.