Lyric discussion by Archangel717 

Cover art for Behold A Pale Horse lyrics by Angels and Airwaves

I think "Such a strange celebration" is stating the irony of when the end of the world comes, people will be happy, instead of fearful and sad.

My Interpretation

@Archangel717 That's exactly what it's referring to. The kids all celebrate as this happens as they are still innocent.