Block Downloads

1. Lock the kids in a different room to the computer.

2. Lock the computer in a different room to the kids.

3. Disconnect the computer from the internet, and place the router or modem in your safe.

In my experience only 3. works.

🙂

Which leaves System Preferences/Parental Controls.

If they have access to the computer with the same
user or Admin account that you do, change it.

Otherwise, they can use any software you can.

A different user account for them, with a login
and other parameters, limited privileges and
access to the system and internet limited, is
about all you can do.

There are some children-protective browsers;
those could be installed on a child's account.

see - ' mac os x children's software web browsers ' - google search:
http://www.google.com/#hl=en&q=macos+x+children%27s+software+webbrowsers&aq=f&aqi=&fp=azWfBBCvguA

You can also use most browsers to not allow content
from specific sites by URL; that control would depend
on the browser(s) in use and how they are set up.

The separate accounts for other users, where
you would also have to log-in to use the Mac,
would be a better idea overall; and then you
can limit access to the hard disk drive, and
the applications, and give them a limited access
and a few items in the Dock. And kid browsers.

This could also save you a lot of trouble should
someone decide to mess with the System or a
few of your important files on the hard drive. It
also would enhance overall security on the Mac.

Good luck & happy computing! 🙂

If the other users have a different account and
can't install applications from anywhere into
the system without an Admin Password, then
they should not be able to damage more than
their own user accounts, anyway.

Some of the applications out there, from odd
sources, could be capable of mischief. Stuff
from unreliable or not trustworthy sources are
prime for someone else's experimentation in
the realm of elementary hacking 101. The use
of an Admin account to play around when an
other option could be preventative action, is
foolhardy; the accounts aren't hard to make.
Just don't give them equal access.

Some of the browsers could be set to not allow
downloads from certain sites, they can block
images and other stuff. Look into preference
settings in your browsers...

Or look for a good older model Mac just for them.

In any event...
Good luck & happy computing! 🙂

Well, you can "ask" your teens NOT to download without your permissions first. Otherwise, threaten them w/Klaus1 recommendations.
I wish to add *#4 remove the keyboard & hide it* to the list. 😉