The two happily posed for pictures along with Levine's Maroon 5 bandmate James Valentine, much to the delight of the young people there.
While at the hospital, Clarkson and Levine also answered questions from kids prior to their Wednesday night concert at the Susquehanna Bank Center.
"Had such a great time visiting the kids at the Children's Hospital of Philadelphia today!" Clarkson tweeted.
Yep. Definitely puts a song in our hearts.