The Switch (2010)

Wally's best friend Kassie resorts to artificial insemination to have a child. Seven years later, Wally is reunited with her and meets little Sebastian. When Wally becomes Sebastian's babysitter, he feels very close to him, as if he were his son, sharing his quirks and eccentricities. A peculiar episode forgotten by Wally at a party clarifies the whole affair. An unconventional dramatic comedy about parenting that is much more than a romantic comedy, with an endearing performance by Jason Bateman.