That's a shame! But that's what kids are like.

I remember when my younger daughter was a preteen wanting to learn piano, she gave up in disgust after about twenty minutes. Her reasoning was that she "couldn't do it!". She fully expected to be able to play fluently as soon as she sat down in front of it - and no amount of persuasion would change her mind.
Leaving her to come back to it herself proved the best option. Given time, the lads may decide to pick it up again. And it's much easier to leave a guitar lying around somewhere to hand than it is a piano.
