Adult Adoption follows Rosy (Moon), a 25-year-old bank teller who aged out of the foster care system at 18 and has since managed to build a stable albeit rudimentary and lonely life for herself; she dresses like a very young girl and eats nothing but Kraft Dinner.

She has a normal human interaction with the owner of the coffeeshop in her building, reaches out to Helen to try to start mending the relationship, and returns to yoga class, where she allows the instructor to reposition her.

[3][11] Tabassum Siddiqui, writing in The Globe & Mail, said that "for all its quirks, at its heart Adult Adoption is a thoughtful coming-of-age story that will have you rooting for its complicated heroine" and designated the film a "Critic's Pick".

[13] Amber Wilkinson, writing for Screen Daily, said that the film "is scattered with many ... little lessons about connections found in unexpected places without labouring the point and embraces the often unexpectedly warm messiness of real life" and is "a showcase for Moon's onscreen abilities"; however, she thought that the film had perhaps "one plot strand too many" and that Moon's background as a writer for stage showed in the script, which "struggles to make the connecting moments between scenes flow freely", but that once the scene had changed, the script "strikes a good balance between everyday absurdity and underlying emotion".

[7] Chris Knight, writing for the National Post, said that "[w]riter and star Ellie Moon crafts a fascinating story about relationships in all their oddity, messiness and necessity" but that the "plot is ultimately a little thin – the cult, for instance, feels a bit too spot-on Handmaid's Tale, and the resolution of that storyline oddly simple – but there is still much to admire".