Here are some ideas, depends on what you want to do...
You can set up your router to block access to specific MAC's at specific times (like, when your kid should be asleep). A MAC is a unique identifier for a specific network adapter. That way, your laptop will work at those times, but the kid's ipod touch will not.
You should be able to set up your router to block specific URL's, maybe even for specific MAC's.
Set up a proxy server for the machines on your network (or maybe just for your kid's ipod touch) to use a blacklist of known "bad" sites. See:
http://dansguardian.org/
These suggestions are great for at home, but won't really work if your kid goes to Starbucks, McDonald's, the mall food court, a friend's house w/ wifi, etc.
Hope this helps!