If this is them in the 1850 US census then all of the children were born in Ireland.

Richard Mason
Age: 46
Estimated Birth Year: abt 1804
Birth Place: Ireland
Gender: Male
Home in 1850 (City,County,State): Moyamensing Ward 4, Philadelphia, Pennsylvania
Family Number: 500
Household Members: Name Age
Richard Mason 46
James Mason 12
Henry Mason 4
Margaret Mason 40
Mary J Mason 18
Catharin Mason 10
Margaret Mason 8
Hannah Mason 2