Penn parish registers have:-
baptised 13 May 1827 William Moorcraft illegitimate son of William Moorcraft, butcher of Beaconsfield, and Sarah Smith of Penn.
baptised 21 Nov 1830 Elizabeth Sarah daughter of Sarah Smith, single woman of Tylers Green.
I can't find any pertinent marriages or burials in Penn - neither can I find a baptism for Walter who states on the censuses that he was born in Penn. As the family had moved away from Penn by 1841 perhaps he was baptised elsewhere?
Jill