I was three… there were five kids and we literally screamed at our parents and said, ‘We are never going to eat meat again.’ Because we were on a boat, and they were catching fish, and they were throwing fish against the side of the boat in order to kill them, they are flopping around … and it was undeniable that it was brutal, barbaric and horrible for us, and so we said that. I remember my mum not being to answer and we said, ‘Why didn’t you tell us that’s where meat came from?’ And she didn’t know what to say. I feel like I have this memory of seeing her crying.

From: https://www.ecorazzi.com/2013/12/02/joaquin-phoenix-tells-story-of-becoming-vegan-at-age-three

Additional article of interest: https://vegnews.com/2020/10/joaquin-phoenix-on-veganism-the-environment-and-social-justice-a-vegnews-exclusive-interview