Don't say, "As Catholics, we are so ashamed."  

It's not Catholicism that caused this to happen, and the abusers didn't abuse because they were Catholic.  Be honest -- as people in a position of power, you abused that power as you abused those in your care.  Be ashamed because you and those like you enabled abuse, tried to hide it, ignored it, put a hierarchy and a clerical system above human beings. 

Those human beings are or were Catholic too.  They have nothing to be ashamed of "as Catholics."