My first thought was yes, and to recommend that you look at the imaging software called “gimp”. However, after looking at the image, it would be very difficult to do and still have a realistic looking sky. There is simply too much text to cover and not much background to “clone” for filling in the blanks. There would be a lot of repeated patches in the sky that would a take some time to smooth out and blend together.
Possible, but not easy. Feel free to try out “gimp”, looking at the “cloning” or “rubber stamp” feature.
Or, alternatvely, you[or he] could try editing the child out of the wallpaper, and super-imposing it on another picture of the starry sky.