Nick,
Maltby seems to be a Lincolnshire name although there are some in Nottinghamshire and Yorkshire (particularly Scarborough). I could not find any further children of John Maltby and Esther in Willoughby in Lincolnshire but did see a child of George Maltby and Esther, a son Thomas, baptised 5 Jul 1781 born 29 December 1780. (FHL film No.989787). George Maltby & Esther Burnett were married 24 May 1773 in Willoughby, Lincolnshire (FHL film No 1541981). So I wonder if the baptism for John in 1778 has been mistranscribed. There is no record included for a John Maltby and Esther in that period.
A John Maltby married in Willoughby in 1823 to Mary Lucretia Lenton.
The two baptisms I gave you yesterday are the only ones in this index with the parents John & Esther Maltby.
Hopefully something in all this will help you.
Nell