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Copied from Ancestry:

Liverpool, Lancashire, England, Marriages and Banns, 1813-1921
about William Henry Thorpe
Name: William Henry Thorpe
Age: Full Age
Marriage Date: 2 Oct 1837
Parish: Toxteth Park St James
Spouse's Name: Mary Ann Nicholls
Father's Name: Filow Thorpe
Spouse Father's Name: William Nicholls

William Henry Thorpe/ full age/bachelor/seaman/Toxteth Park/father Filow Thorpe, Attorney
Mary Ann Nicholls/ full age/spinster/Toxteth Park/father William Nicholls, joiner.

William signed Thorp without an e.
Mary signed Nichols with one l.
Witnesses: John Harris+Elizabeth Harris

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I can't see an IGI baptism for a Mary Ann Nicholl circa 1816. There are 6 Douglas baptisms for Nicholl children born to a William Nicholl and a Cath Quayle:

Margaret 1801
Catherine 1803
John 1808
Robert 1811
Robert 1812
Jane 1819

But I think that yours is probably a daughter of William Nicholls and Jane Costain, because several of their children were all baptised at the same session in 1822:

Robert, Thomas, William, Margaret, Mary Ann

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Name: Mary Ann Nichol
Gender: Female
Baptism/Christening Date: 25 Aug 1822
Baptism/Christening Place: SAINT MATHEWS,DOUGLAS,ISLE OF MAN,ENGLAND
Birth Date:
Birthplace:
Death Date:
Name Note:
Race:
Father's Name: Wm Nichol
Father's Birthplace:
Father's Age:
Mother's Name: Jane Costian
Mother's Birthplace:
Mother's Age:
Indexing Project (Batch) Number: C03804-1
System Origin: England-ODM
Source Film Number: 106186, 106718
Reference Number:

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But no indication of the age of each child at baptism.

Jean C