"Senator Santorum will not hold any campaign related events on Monday so that he and Karen can remain in the hospital with their daughter Bella," campaign spokesman Hogan Gidley said in a statement Sunday.
Santorum's youngest daughter suffers from Trisomy 18, a rare genetic disorder that is fatal for about 90 percent of children before or during birth. It's unclear why the 3-year-old was hospitalized Friday, ABC News said.
This is the toddler's second hospitalization in three months -- she was admitted in January with pneumonia and Santorum briefly suspended his campaign at the time.
Santorum's campaign had announced earlier Saturday the candidate would attend events this upcoming weeks in his home state of Pennsylvania and Missouri, The Hill reported Sunday.
Having been swept by Mitt Romney in three primaries Tuesday, Santorum's campaign said a victor in Pennsylvania is "vital."