No problem.
It sounds like both of your computers are trying to use the same IP Address. As far as I know, this is fine as long as only one PC attempts to use the internet. Obviously, this is an inconvenience which can and should be fixed.
To test the accuracy of my educated guess, please go to Start > Run on each computer, and type cmd, and click OK or press Enter. A black window should pop up. Type the following command as it is, and press Enter:
ipconfig
This should show three pieces of vital information: IP Address, Subnet Mask, and Default Gateway.
The mask is irrelevant. The Default Gateway should be too, but just for kicks, know that the Default Gateway should, if memory serves, be the same as your IP Address (assuming you have a router, which you do) except with a 1 at the end instead of another number.
This is the important part -- if everything is working correctly,
the IP Addresses on the two machines should be different. For example, your PC, the one with the router, should have something similar to
123.456.7.890
Obviously, it will be different.
Your son should have a similar IP Address, identical on the first three fields, but with a different final sequence of numbers. Let us know if they are different, or identical.
IMPORTANT: Do not post your actual IP Address. This is a dangerous practice. If you must, post only the last three digits, since you cannot be tracked by only three numbers.Besides, the first three fields should be the same on both machines anyway -- we don't need to know that.