My kids would rather play with a can of Silly String than even their most expensive toys, and I suspect that mine aren't the only ones. It is a an item commonly encountered at almost any event hosted for children and teens. The biggest problem most folks have is that somehow Silly String always seems to find its way home with the kids, and then magically appears dried on the walls shortly thereafter.
Remove as much of the Silly String from the wall as possible by picking it off by hand.
Wipe the cleared area with a towel moistened with the mild cleaning solution.
Allow the area to dry. If this has not removed the stain, proceed to Step 4.
Gently sand the stained area with fine sandpaper, taking care to not remove any more of the surface than is necessary.
Remove the excess dust from sanding with a towel slightly dampened with water.
Finish the sanded area of the wall with the brush and touch-up paint, and allow it to dry. Repeat this step if necessary.