I agree, I would call OCaml, Haskell, and Rust cousins, more or less ... descendants of ML.

Though the original Rust compiler was written in OCaml, so depending on your viewpoint it could also be its child. I'm not sure if Rust lifted any features or syntax from OCaml specifically. I think the "O" in OCaml was not influential ...

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edit: I found a list of influences, and it does credit Haskell with typeclasses, but SML/OCaml and C++ are credited first:

https://doc.rust-lang.org/reference/influences.html

I always thought of Rust as a mashup of OCaml and C++, but Haskell is in there too.