Easter egger or ameraucana

[Auntiejessi3]

x2 on the Welsummers

Just saying...danger Will Robinson, danger

 

[Iluveggers]

I know you have a list already, and I think Cochins are super friendly & docile, but with a 3 year old I will second the recommendation for Orpingtons. They come in a variety of colors and are generally quiet, sweet, gentle & good with kids. I say generally because personalities do differ but overall they are known for being a very sweet breed.
Easter Eggers will give you blue or green eggs usually, which would be a nice pop of color, and Marans, especially Black Cooper will lay darker brown eggs.

I hope that helps! (& forgive me for adding a breed you didn’t have listed, I just couldn’t not say anything!)