just a little bit of info - Isabella was BAPTISED 19th Feb 1847 -n probably born about a week earlier
Baptism: 19 Feb 1847 St Laurence, Chorley, Lancashire, England
Isabella Warburton - [Child] of Thomas Warburton & Nancy
Abode: Chorley
Occupation: Crofter
Baptised by: H. Sewell
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siblings Baptism: 7 Feb 1836 St Laurence, Chorley, Lancashire, England
John Warburton - [Child] of Thomas Warburton & Nancy
Abode: Chorley
Occupation: Bleacher
Baptised by: Wm Wignall
Register: Baptisms 1836 - 1851, Page 5
Source: LDS Film 1517686
Baptism: 2 Sep 1838 St Laurence, Chorley, Lancashire, England
William Warburton - Son of Thomas Warburton & Nancy
Abode: Chorley
Occupation: Finisher Bleacher
Baptised by: John Kendall
Register: Baptisms 1836 - 1851, Page 91
Source: LDS Film 1517686
Baptism: 18 Sep 1840 St Laurence, Chorley, Lancashire, England
Mary Warburton - [Child] of Thomas Warburton & Nancy
Abode: Chorley
Occupation: Bleacher
Baptised by: J. S. Master
Register: Baptisms 1836 - 1851, Page 138
Source: LDS Film 1517686
.....................................
different church and 5 years later - but still in Chorley - another possible sibling
Baptism: 5 Apr 1852 St Peter, Chorley, Lancashire, England
Eliza Warburton - [Child] of Thomas Warburton & Nancy
Abode: Chorley
Occupation: Labourer
Baptised by: H. Sewell
Register: Baptisms 1851 - 1900, Page 7, Entry 55
..................................
probable marriage for Thomas and Nancy
Marriage: 2 Mar 1834 St Andrew, Leyland, Lancashire, England
Thomas Warburton - Bachelor, Leyland
Nancy Warburton - (X), Spinster, Leyland
Witness: Elizabeth Warburton, (X); John Warburton, (X)
Married by Banns by: Thomas Rowlandson Curate
Register: Marriages 1834 - 1837, Page 7, Entry 21
Source: LDS Film 93953
.....................................................but you say both born in Chorley ? maybe that marriage isn't your Thomas and Nancy - but it is the only marriage I can find for that era