Question: The center I volunteer for has received 22 Window 7 Professional PCs and a printer, all are networked to a 24 port D-Link switch.

What software could I use to configure multiple PCs at the same time. For example install software, configure system settings and also restrict access to certain websites (it is a children center).

The software has to be open source as we do not have any funds to purchase any licenses.

Answer: 
Active Directory running on Windows Server would be your best bet. Failing that there are a mass of open source options for doing a lot of this stuff.

Microsoft offers discounts for registered non-profits, and if you can make friends with someone at Microsoft, you can probably get them to give you all sorts of good stuff.
There is a microsoft free software [Microsoft SteadyState](http://www.microsoft.com/downloads/en/details.aspx?familyid=d077a52d-93e9-4b02-bd95-9d770ccdb431&displaylang=en) that can be used to lock down the configuration of the PC, i haven't used it in a production enviroment but it seemed ok so far, let us know how it works out