<P> In addition to his children , Frank is also a loving grandfather to Erin 's daughter , Nicky Reagan - Boyle ( Sami Gayle ) , and Danny 's two children , Jack ( Tony Terraciano ) and Sean Reagan ( Andrew Terraciano ) . In one episode , it is mentioned that Frank 's wife 's grandfather was one of the builders on the Brooklyn Bridge in the 1870s and ' 80s . Frank 's dad 's father , Charles Reagan , was an Irish immigrant who served in World War I before becoming a police officer . Charles was the one who taught him how to fish . In `` Whistle Blower '' ( season 2 , episode 10 ) , Frank mentions his great - uncle Teddy Reagan , a member of the NYPD Mounted Unit , who spent a cold night in a boxcar with his horse , Dolly , and woke up in Pittsburgh . </P>
<P> In addition to his children , Frank is also a loving grandfather to Erin 's daughter , Nicky Reagan - Boyle ( Sami Gayle ) , and Danny 's two children , Jack ( Tony Terraciano ) and Sean Reagan ( Andrew Terraciano ) . In one episode , it is mentioned that Frank 's wife 's grandfather was one of the builders on the Brooklyn Bridge in the 1870s and ' 80s . Frank 's dad 's father , Charles Reagan , was an Irish immigrant who served in World War I before becoming a police officer . Charles was the one who taught him how to fish . In `` Whistle Blower '' ( season 2 , episode 10 ) , Frank mentions his great - uncle Teddy Reagan , a member of the NYPD Mounted Unit , who spent a cold night in a boxcar with his horse , Dolly , and woke up in Pittsburgh . </P>
who plays danny reagan 's sons on blue bloods
who plays danny reagan 's sons on blue bloods
Tony Terraciano Andrew Terraciano
Tony Terraciano Andrew Terraciano