I have in my "Spares Database" George Willis son of Henry and Elizabeth baptised 10 Sep 1748 at Shalford, you no doubt have that info.
Again from my Spares Database I have a Henry Willis who married Elizabeth Bird at Black Notley, both were noted as being of Shalford, are this couple yours?
My ancestors who were having children around the time of your George being baptised in 1748 were Edward Willis and his wife Sarah Joyce, their children, all baptised in Shalford:-
Edward 1725.
Sarah 1725.
John 1740, aged 10.
Thomas 1740, aged 8.
Joseph 1740, aged 5.
Elizabeth 1740, aged 2.
The parents of Sarah Joyce were Samuel Joyce and Hannah Rust, I would have expected Edward and Sarah to name children Samuel and Hannah so perhaps there are other children baptised in some other parish.
I have another Willis line which were based in Felsted and Great Saling.