This kid...
Liam James, is now listed on imdb as rumored to be playing Sam.

ETA: There is also a post on imdb that says Charlie Tahan was cast as Sam:

We'll have to wait and see I guess what the trades say I guess.
Also, kind of random, but Zac signed some Havaiana flips for part of a silent auction for the Second Annual PacSun Pipeline to a Cure Gala this weekend. The organization raises money and awareness for the Cystic Fibrosis Foundation.
ETA: There is also a post on imdb that says Charlie Tahan was cast as Sam:
We'll have to wait and see I guess what the trades say I guess.
Also, kind of random, but Zac signed some Havaiana flips for part of a silent auction for the Second Annual PacSun Pipeline to a Cure Gala this weekend. The organization raises money and awareness for the Cystic Fibrosis Foundation.