I already have a story for this, though the kid is a girl and the imaginary friend is trying to pursue a romantic relationship (despite the feelings being one-sided/the fact that's impossible.) <<that sounds so sweet!
And now, pick a number between 1 and Instant writing prompt. :D - I actually started reading this as chapter titles XD now THAT would be one crazy story. Looks like a fun creative-writing exercise for the kiddos