Original image

step 1 of 9

step 2 of 9

step 3 of 9

step 4 of 9
Used standar pattern copy tool to cover some of the excess blue sky behind the trees on the right side of the image.

- : source
step 5 of 9
Also masked the horizontal tube, to make it look like a proper glass corridor.

step 6 of 9
Added shadows for the glass and shapes with drop shadow effect and layer duplicating (when drop shadow effect gave bad results).
Gave the shapes and glass some depth with inner shadow effect, to make them look more round and 3D.

step 7 of 9
I masked some of the areas to hide excess colours and highlight certain areas.
Used pattern tool for the colouring image too, when I wanted to repeat certain colours (like more red on some areas)
The direction of the 'main light source' changed, so I decided to cover the actual sun, to make it appear the sun is shining behind the observer view point. Otherwise I should have added the shadows in front of the picture and didn't feel comfortable with the idea.

- 1: source 1
step 8 of 9
I made a copy of the boy, made him a new straight leg (like not walking) with pattern tool and colored his shirt with gradient map and hue/saturation tools. Also removed that strange red candy bag or w'ever he was carrying in his pocket.
For the girl I altered the colours to fit better the picture.

step 9 of 9
Took a duplicate of the whole layer, used render/lightning to colorize the new layer and with masking and blending options adjusted the final colours to appeal for my eye.

Final result

