In an online statement, the family asked for privacy.
"Our little girl is a fighter and is improving each and every day," the statement said. "We appreciate your patience, love and support, as we too are stunned and saddened by this tragedy."
A cyclist found the girl, a student at Horning Middle School, bleeding on a sidewalk Saturday. Hours later, Morgan Geyser and Anissa Weier, both 12, were found by a Waukesha County sheriff's deputy walking near I-94.
In a criminal complaint, authorities said the attack left the victim "one millimeter away from certain death."
Geyser and Weier, who have been charged as adults with attempted murder, allegedly told detectives they were trying to please Slender Man, a character on the Creepypasta horror website. They spent Friday night on a sleepover at Geyser's home with the victim and said they stabbed her in a park the next day.
The victim had 19 wounds. Waukesha Memorial Hospital said Wednesday she was listed in fair condition.
Her parents, in a statement on a fundraising site, said the girl is now well enough to sit up to watch televison and to walk supported by her father.