DD arrived home last week, exhausted from hiccupping all afternoon. We googled & had a laugh at all the "cures", then found one that sounded promising, tried it & instant stop.
Last night DS started. I told him what to do, he laughed & had NO MORE hiccups - instantly. It's fab.
Basically, you have to concentrate & wait for the next hic. You must try & say something (we used "beep" just as/before you hiccip. Apparantly it might take 2 or 3 hics for you to get it, but neither of my kids had a single one - they just sat & waited for it (whilst laughing at how silly it was).
Next time you or kids suffer, try this & report back here :)