Hi Michele,
If you don't want to have digitally altered versions of your painting in this thread, feel free to remove this.
I tried to change certain things in your painting to show what might take you closer to Sargent. These are just suggestions, of course.
I darkened the whole image and made the white clothing of the girl lighter, so there is a sharper, more dramatic contrast.
I made the pants of the boy black, instead of blue. Both children have blue pants in the original version, but making the boys pants black makes a stronger division in
values.
I made the seat lighter on the right side, this gives an opportunity to get a very dynamic brush-work in the painting. And creates a more spatial impression, I think.
I made the pants of the girl of a deeper blue, and made it darker in some areas.
I created a 'line of light' in the edge of the white pages of the book.
In the background, with the Sargent as an example I made the red background even warmer and lighter.
I made the shadow-side of the children's faces warmer.
The grey clothing of the boy, I made it a little bit darker.
I darkened the foot of the boy a little bit, and lightened the hand of the boy a little bit.
I darkened certain pieces of the painting in the background, and lightened other pieces.
I darkened the left side of the seat a little bit.
Of course, this is easier than painting it
I really like your painting as it is, but you asked for it !
Peter