Start here:
On caring (Nate Soares, 2014)
The psychology of existential risk and long-termism (Stefan Schubert, 2018)
Why we have to lie to ourselves about why we do what we do (Robin Hanson, 2018)
Further reading:
Replacing guilt (Nate Soares, 2015)
The value of a life (Nate Soares, 2015)
Purchase fuzzies and utilons separately (Eliezer Yudkowsky, 2009)
Altruistic motivation based on pain vs enjoyment (Brian Tomasik, 2017)
Tradeoffs (Julia Wise, 2014)
Aim high, even if you fall short (Julia Wise, 2014)
Purchase fuzzies and utilons separately (Eliezer Yudkowsky, 2009)
Mr Rogers on unconditional love (Brian Tomasik, 2013)
Effective altruism complaints (Robin Hanson, 2015)
The Elephant in the Brain (Simler and Hanson, 2018)
We are in triage every second of every day by Holly Elmore
The Moral Imperative toward Cost-Effectiveness in Global Health by Toby Ord
Fear and Loathing at Effective Altruism Global 2017 by Scott Alexander
And I'm sure you can find plenty by Peter Singer, including full books. Here are a few short reads:
The Drowning Child and the Expanding Circle
Famine, affluence and morality
https://www.philosophyexperiments.com/singer/ (a questionnaire based on Singer's drowning child thought experiment)
https://schwitzsplinters.blogspot.com/2020/06/contest-winner-philosophical-argument.html
There's also his introductory TED talk.
Also: Charity: The video game that’s real, by Holden Karnofsky
FYI Purchase fuzzies and utilons separately is showing up twice in the list.