The Internet is a scary place. Now, I'm not a parent yet--but if I were, I'd want to at least try to impose some realistic limits on the internet for my kids. I'm not into shielding kids from too much, but some things (and some sites) just cannot be un-seen, as you may possibly know but not care to admit. Plus, it's probably nice to know that your kids can't browse the Internet a 3 in the morning when they have school in only a few hours.
Fortunately, if you have a WNR3500L, you can use Toastman's excellent Tomato firmware build to set up a variety of settings to restrict Internet access on your router. Here's how.
If you haven't snagged the latest version of Toastman's Tomato build for your WNR3500L, you'll need it to proceed. Click here to download it, and here for information on how to install it before proceeding.
[Purchase a NETGEAR WNR3500L]
Monitoring Web Usage
If you don't want to restrict usage in your household--but would like an idea of what's going on, this firmware has the ability to track virtually all Internet activity going through the router. It's automatic and easy to set up.

Head over to the administration panel, then "Logging." Simply check the "Monitor Web Usage" option. You can select to monitor all machines, or select an individual machine, as well as how many line items to remember.
In this way, you can see what sites are being accessed by your Internet connection.
Blocking Access Entirely
These days, it's probably an extremely severe form of punishment to banish a kid from the Internet. I know if I had to go without for more than a day, I'd probably explode. Here's how to block access entirely to a certain machine.

Head to the Basic => Wireless Filter panel. From here, you can enter the MAC address of the unique machine or machines you would like to add to the block list.

Unsure which devices are which? You can head to the Basic => Device List panel and see the MAC and IP addresses of each device connected to your network, sometimes with a device name or description.
Of course, there are probably creative ways around this MAC address restriction, but if your kid figures out how to do this, perhaps they have a career in programming, engineering, or a similar geeky field ahead of them :)
Scheduled Access Restriction
You can also restrict access by day and time. This is useful if you actually want your kids to go to bed at a certain time instead of staying up and playing Minecraft all night, which is what I would have done had Minecraft existed in the 80's.

In the Access Restriction panel, you have the ability once again to set up rules for all machines or for specific MAC addresses. You can set up a time and date schedule to restrict access. Pretty simple!
Restricting Certain Sites or Activities
Perhaps you don't care as much about scheduling timed restrictions, but more about certain sites--say your child is particularly fond of Miniclip and they are now grounded from it, or there was a particularly nefarious domain you caught them peeping at once.

Simply uncheck the "Block All Internet Access" option at the bottom of the Access Restrictions screen and you'll see a whole new pane of options pop up. There's a TON of custom options available here--you can block certain sites or certain types of traffic (e.g., P2P, etc.)
Conclusions
In addition to being a robust firmware on its own, I was surprised to see the multitude of restriction options in this firmware. It's so easy to use and install, and with these options, I can heartily recommend it as a firmware ideal for family home use.
[Purchase a NETGEAR WNR3500L]