Amplitude (noun) is the distance of an object (or, more often, person) relative to the nearest amp. (see amp)
Because an amp is an almost sickeningly well-behaved child, a short amplitude is generally to be welcomed, or at least not unpleasant, unless, of course, you don’t want to be almost sickened.
Then again, sometimes you don’t have a choice about your amplitude, particularly if it is your child. Well, look on the bright side. Your child could have been an imp rather than an amp. So there’s that.