Quick job, quick step by step:
1. Masking, in this case I used twice ''color range selection with indication on the middle and edge of bright grass. Filling new layer with darker green (taken out of photo) and then playing with multiply
mode set up brightness. Then you can change hue to match a tone or use one more layer with color
mode. Also it could be good to have one more, greyscale leyer in multiply
mode with high contrast to bring back texture (I havent done it here)
Dont forget to cut green colour popping up on children bodies. I have forgoten do it on their hands
2. Then masking edges, grab a piece of grass beside, drop over and with sofr eraser cut its edges so it blends easly. You can see, I have done some parts (right from boy's head) other partly or not at all, to show effect.
3. Once it is done, apply warmth filter. Or do it in RAW procesing software before.
4. Play a bit with curves (just a bit) and then apply a touch of saturation.
5. Slight sharpenig also will help, especially if you will mask only children.
6. Dont forget to convert to srg space if you want to publish it on the web
Regards,
K.Polak