The 29-year-old headed to the Floating Hospital for Children at Tufts Medical Center in Boston and helped boost the spirits of young patients by touring the wards, reported OK magazine online.
"She met sick youngsters and their families and signed CDs for them and even treated the kids to an impromptu performance of Twinkle, Twinkle Little Star after a two year old requested the song," a source said.
"Met a brave young lady and fellow songwriter today named Chloi. Such a positive spirit! So sweet," Underwood tweeted.
"We are so grateful to Carrie for partnering with us to bring this one-of-a-kind experience to the children and families at Floating Hospital," she further tweeted.
