"even darkness must pass. a new day will come. and when the sun shines it will shine out the clearer. those were the stories that stayed with you. that meant something, even if you were too small to understand why. but I think, mr. frodo, i do understand. i know now. folk in those stories had lots of chances of turning back, only they didn’t. they kept going, because they were holding on to something.”
Time For The Stars by Robert A. Heinlein. All of Heinlein's juvenile sci-fi novels pretty much rocked. This one had twins, telepathy, and one twin aging at a different rate, due to near-light-speed travel!