My five year old son said he would call his unicorn 'Leon'. Translated to english: 'Lion'.
I asked him twice. He seemed pretty sure about it.
If you use music, this can be the theme song: [ame=http://www.youtube.com/watch?v=Dk3iik_GPZE&feature=related]YouTube - Unicorn Song - Agnes - Despicable Me[/ame]