ᐅ Making Staircases and Wallpaper Child-Safe?

Hello,
we moved into our new house at the beginning of 2016. Now I will soon be on parental leave again and want to address the following "problem" during this time:

We wallpapered our stairway (half-turn staircase) with a white non-woven wallpaper. This has unfortunately proven not to be very practical by now (three children – 8, 2, and 5 months old). The wallpaper in this area is already marked by little hands. I have already applied a latex primer once... but it was partly too late, and it doesn’t provide full protection anyway.

Simply painting it white is not an option since the wallpaper has a subtle pattern. Leaving it as it is doesn't look good either, in my opinion.

I have already thought about covering it with decorative film or maybe even a photo wallpaper with a nice motif. But perhaps you have an idea of how I could design it?

The installation is obviously tricky because the staircase isn’t straight, so reaching the right height with a ladder is difficult... maybe someone has a tip for that as well? The worst area is about 1.20m (4 feet) above the stairs...

I would probably just apply a wide colored strip running parallel to the handrail.

This is probably the least work... although I do have to consider the slope of the staircase... let’s see if I can manage to do it fairly neatly...