personally i love the sidewalk chalk. it's washes off with a water hose. and it's MUCH better then pen marks all over my walls. which, by the way is what i'll be scrubbing off MY walls all day today
two years ago....my kids went crazy with sidewalk chalk all over the 3 unit property. now, the owner has kids too, so i didn't think it would be such an issue. my husband at the time thought it would be (he never had kids at that point). he freaked out. then i pulled out the hose, washed it off. he looked a bit silly after that. the next day, my kids went to play with the owner's kids....totally wrote all over the driveway, all over the building steps. my husband grimanced and walked away. the owner came out and inspected the artwork. totally loved it.
now the issue might just not be the artwork itself....but the noise the children are making under the window...
but i totally dig the sidewalk chalk party idea!!!