Full Idea
We do not speak of an ox or a horse as happy, because none of them can take part in fine deeds; similarly, no child is happy, because its age debars it as yet from such activities.
Gist of Idea
Oxen, horses and children cannot be happy, because they cannot perform fine deeds
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1099b32)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.81
A Reaction
This is a place where 'happy' is not a very good translation for 'eudaimon', as we universally acknowledge a 'happy childhood'. We can have a 'successful' life, but not a successful childhood. I'm not convinced that even Greeks understood 'eudaimonia'.