Brian Lawson's website has several children of James and Harriet listed with their birth registration references, and their certs (or one cert) can be ordered by email from the Registry: http://www.gov.im/registries/general/civilregistry/
The certs will give more detailed information about their parents.
SAYLE, Ada, [born] 23 Mar 1885 Dou [father] SAYLE, James, [mother] MC DONALD, Harriett.
SAYLE, Clara, 27 Oct 1888 Dou., SAYLE, James, MC DONALD, Harriet.
SAYLE, Emily Jane, 19 Apr 1883 Dou, SAYLE, James, MC DONALD, Harriet .
SAYLE, Harriet , 7 Jan 1882 Dou, SAYLE, James, MC DONALD, Harriet.
SAYLE, James Alfred, 28 Jul 1894 Dou , SAYLE, James, MC DONALD, Harriet.
SAYLE, Mabel Edith, 21 Apr 1886 Dou, SAYLE, James, MC DONALD, Harriet.
SAYLE, Mary Jane, 28 Jan 1880 Dou, SAYLE, James, MC DONALD, Harriett.
SAYLE, Thomas, 23 Feb 1891 Dou, SAYLE, James, MC DONALD, Harriet.

http://www.lawsons.ca/births/sayle.html

These are all later children because civil registration of births in the IOM was compulsory only from 1878. But the details of these children's births should still give you good information.

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