Personally, I think it is a good idea to have kids learn piano for at least a couple of reasons. First, I think the visual layout of a piano can help attach a physical understanding to the concept of intervals and chords (specifically the distance between notes, and the clustering of notes in specific patterns to form chords). For me personally, I think that was a benefit, even though I play piano very little, and not very well. Secondly, I don't recall ever meeting an adult who took lessons as a child for any length of time (and then quit) who as an adult does not wish they had continued. Now surely there will be at least 7 people on HN who will now speak up, inform me that they hated lessons as a child, happily quit when they were able and never regretted it for a second. But unless my memory is failing me, that must mean we've never met (or at least we've never discussed piano lessons), and thus my statement still stands :-D To that I will add, that even with a number of "I quit and I'm glad" entries, I still think the majority of the adults in question wish they hadn't quit.
Oh, and a third reason to play piano: they make nice weighted, touch-sensitive keybords now that do a pretty decent job of mimicking the feel of a real piano (at least close enough for me), and you can move them from room to room and house to house by yourself. (You won't have to get 3 to 5 of your soon to be ex-best friends to help you). We sold our old upright piano about 3 moves ago, and I've been celebrating the sale ever since :-D