I assume they have lectured their siblings about it and remind them regularly of the rules since Peter is only now starting to read and the other two boys aren't even that good at listening. Plus it's not posted low enough for them to read it.
No doubt the girls want to keep their room tidy so they can do their school-work without being distracted by clothes and toys on the floor, fighting brothers, etc.
I'll be sure to post any updates to the rules here (subject to change at any time) and any spectacular breaking of the rules in the mean time.
