Make sure the computer you (and your children) use is properly protected. Think twice about what you do with public computers; you don't know how well maintained they are, or who's been using them.
Check the essentials in Windows Security Center
Check that you have ONE firewall program installed and running
Check that your computer is set to use Windows Update
Check that you have ONE antivirus program installed, running and up-to-date
Other Steps:
Check that you have up-to-date versions of other software, such as Adobe Flash
Stay away from File Sharing programs
Make a backup of your important documents and photos
Only connect to safe Wireless Networks
If you have children, take extra precautions to protect your Child's PC