The name self-indulgence is applied also to childish faults; for they bear a certain resemblance to what we have been considering. Which is called after which, makes no difference to our present purpose; plainly, however, the later is called after the earlier. The transference of the name seems not a bad one; for that which desires what is base and which develops quickly ought to be kept in a chastened condition, and these characteristics belong above all to appetite and to the child, since children in fact live at the beck and call of appetite, and it is in them that the desire for what is pleasant is strongest. (bold mine)
Aristotle (from the Nicomachean Ethics, Written 350 B.C.E, Translated by W. D. Ross)
This is so true, the part I put in bold. Children are happy as long as life is going their way, and as soon as challenges and difficulties arise, they are unhappy.