Lavigne went to the Mattel Children's hospital in Ucla, California, last month and took some musical instruments along with her for the children to learn while they recover.
The 27-year-old singer and her musician pal Evan Taubenfeld helped teach their young proteges the basics. Lavigne shared her excitement on Twitter.
"EvanT giving impromptu guitar lesson (at) UclaHealth Mattel Children's! We just donated instruments 2 them (sic)," she tweeted.
"Thank you Evant for helping The Avril Foundation donate instruments (at) Ucla Health Mattel Children's," she added. Lavigne had earlier visited the facility in April, and had met the kids in the wards and even performed for them.