As part of the Chan Zuckerberg Initiative, the couple will fund disease research, they wrote in the note.
"Our initial areas of focus will be personalized learning, curing disease, connecting people and building strong communities," they wrote.
Zuckerberg and Chan pledged to give 99% of their Facebook shares, worth about $45 billion, to the initiative, with likely a few billion of that going toward developing cures for diseases.
"Once we recognize that your generation and your children's generation may not have to suffer from disease, we collectively have a responsibility to tilt our investments a bit more towards the future to make this reality. Your mother and I want to do our part."
Zuckerberg and Chan were pragmatic about advancing disease treatments and cures.
"Curing disease will take time. Over short periods of five or ten years, it may not seem like we're making much of a difference. But over the long term, seeds planted now will grow, and one day, you or your children will see what we can only imagine: a world without suffering from disease."
With $45 billion to give away, and with health research getting some part of that, the world likely be a healthier place for baby Max.