Two big Hollywood stars made headlines this week not because of their latest projects but because they showed just how much they care about their respective communities.

"Iron Man" star Robert Downey Jr. took some time out to present a 7-year-old boy with a bionic arm, The Associated Press reported. Two-time Oscar winner Tom Hanks, on the other hand, helped Girl Scouts sell cookies in the San Francisco Bay Area, according to the New York Daily News.

Downey, dressed in character as hero Tony Stark, opened up a pair of metal cases marked "Stark Industries" to present Alex with a working bionic prosthesis.

"I'm another bionics expert on hand, so I thought I'd drop by," Downey said as he met the boy, who was born with a partially developed right arm. The encounter was captured on a YouTube video that went viral almost immediately.

The arm Alex received was made by Albert Manero, an engineering student who donates 3D-printed bionic limbs to kids around the world. Manero's company, Limbitless Solutions, hopes to eventually equip diplomatic missions with the printers so children who live in countries without advanced medicine can benefit from his designs.

Hanks' good deed of the week, meanwhile, seems to have been a bit more spontaneous: The actor, accompanied by his son, Truman, a freshman at Stanford University, spotted the Girl Scouts selling cookies and decided to not only buy some but help the kids with their marketing efforts.

The actor offered to pose for pictures with buyers and then took home four boxes himself; he also donated an additional $20.

Archana Appanna, the mother of one of the girls, told the Los Altos Town Crier that the group almost did not recognize the "Forrest Gump" actor. The woman, who grew up in India, said she was a fan of "Sleepless in Seattle" and "You've Got Mail," two movies in which Hanks starred alongside Meg Ryan.

"I'm still on cloud nine. We did not know who he was (at first) because he covered his face with a baseball cap and glasses," Appanna said. "He was so personable, so down to earth."