Adjective : a trusting child.    From Dictionary.com. 

Kate had rapidly grown old; the look of radiant happiness and trustingness was gone.    From Wordnik.com.  [Blackwood's Edinburgh Magazine, Volume 62, Number 385. November, 1847.] Reference

That rottenness counts on the trustingness as well as the apathy and/or cynicism of individual citizens.    From Wordnik.com.  [Poll: Outright Majority of Democrats Back Hillary] Reference

From the dictionary, perfidy is defined as "violation of a trust reposed", "from phrase per fidem decipere 'to deceive through trustingness'", "calculated violation of trust; treachery".    From Wordnik.com.  [They just can't resist reaching for the sensational] Reference

Sure there is no bound to the trustingness of women.    From Wordnik.com.  [The History of Henry Esmond, Esq. A Colonel in the Service of Her Majesty Queen Anne] Reference

There was a remarkable trustingness, if I may so speak, in Madeline's disposition.    From Wordnik.com.  [Eugene Aram — Complete] Reference

But all the habits of his life, his taste, his associations, his education - every thing - the trustingness of his disposition - his want.    From Wordnik.com.  [The flush times of Alabama and Mississippi : a series of sketches,] Reference

I wiped them then, and Eliza stood like a trusting child as I did so; and when I said I could not leave her till she smiled, she did smile a radiant smile of hope and trustingness.    From Wordnik.com.  [Recollections of a Southern matron,] Reference

In calculations on the character of the Moor, Iago despises Othello's unsuspicious trustingness as imbecility, while he hates him as a man because his nature is the perpetual opposite and perpetual reproach of his own.    From Wordnik.com.  [Short Studies on Great Subjects] Reference

In his calculations on the character of the Moor, he despises his unsuspicious trustingness as imbecility, while he hates him as a man because his nature is the perpetual opposite and perpetual reproach of his own.    From Wordnik.com.  [Froude's Essays in Literature and History With Introduction by Hilaire Belloc] Reference

"Oh," I cried, "for the uplifting faith that hath so often blest me! oh for the hopefulness, the trustingness of times past!.    From Wordnik.com.  [Autobiography of a female slave,] Reference

) and of course oxytocin is the hormone associated with love/pair-bonding, and also with trustingness.    From Wordnik.com.  [Planet Atheism] Reference