You can hear the auto-tune pitch correction in that Celtic Woman clip, not pleasant IMO.

As for the young girl, it's not the kind of thing I dig but her pitching is good and her voice is strong all round. She does sound a tad over-coached to me, hopefully as she matures and the 'young prodigy' media hoo-haa dies down, she'll settle into her own mature voice and a decent adult career.