These laws will not help. Outlawing content will not make it suddenly disappear, it will just be a bit harder to find. Any attempt to filter content will be circumvented. Australia's attempt failed miserably back in 2007[1]. I agree that children are exposed to too much "crap" today, but using children as an excuse to censor material is a political move.
I grew up in a country with mandatory web filtering. ("For pornography", but naturally, dissent forums always end up in that list.) Virtually every kid I knew was comfortable using Tor, Bittorrent, or a plain old web proxy (in the early days) to get around it.
These filters are just an inconvenience, and if your child is too stupid to work around them then you've got worse problems.
[1]: http://www.schneier.com/blog/archives/2007/08/australian_por...