Indeed John & Mary Ann had a son: James Dicker b 1840 Yealmpton, Devon d Aug 1901, Tasmania
John Dicker and Elizabeth Taylor had a son John aka Jack b 1877 Creacombe, Holbeton, Devon who died 1963 Gumeracha, this is the John that married Mary Honor Watts. They had an unnamed son - stillborn 10 May 1879 whilst travelling on the vessel 'Holmesdale'.
I have not verified this for myself, but the info comes from someone who has researched extensively, but it is a little confusing as they seemed to name their sons John, Joseph and William on a regular basis. I am still unsure as to whether the John Dicker who married Elizabeth Taylor was born in 1835 or 1840. It will be some time before I get round to checking this.
Hope this helps, anything else please feel free to contact me. Best regards. Rowland