I Am Sam

Sam Dawson has the mental capacity of a 7-year-old. He works at a Starbucks and is obsessed with the Beatles. He has a daughter with a homeless woman; she abandons them as soon as they leave the hospital. He names his daughter Lucy Diamond (after the Beatles song), and raises her. But as she reaches age 7 herself, Sam's limitations start to become a problem at school; she's intentionally holding back to avoid looking smarter than him. The authorities take her away, and Sam shames high-priced lawyer Rita Harrison into taking his case pro bono. In the process, he teaches her a great deal about love, and whether it's really all you need.

I Am Sam is a 2001 drama telling the story of a mentally challenged father and his efforts to retain custody of his daughter.

Source: Wikipedia