Chris Pratt, Anna Faris Double Date with Son and New Mates for Trick-or-Treating

Chris Pratt and Anna Faris are doing divorce as well as ANY Hollywood couple ever has -- cause they went trick-or-treating together ... WITH their new significant others, and everyone was all smiles!

The freshly divorced duo, along with Katherine Schwarzenegger and Michael Barrett, took Jack out for Halloween in full couples costumes too. Chris and Katherine were Vikings, while Anna was Snow White and Michael took a shot at Khaleesi from 'GoT.' Jack was cool as ever as a ninja.

Costumes aside ... ya gotta check out the gallery, because not only are Chris and Anna getting along -- but Anna and Katherine were chummy and laughing. Bonus for Chris! Always better when the ex and the GF get along.

The modern fam was so NOT awkward, Chris and Kat were even sucking face during the outing.

As we reported ... Chris and Anna officially finalized their divorce two weeks ago.

This is becoming a thing in Hollywood -- we just saw Orlando Bloom, Katy Perry and Miranda Kerr chopping it up.