Are you aware that there may be a registered sex offender in your area? It might very well be possible that a sex offender was recently released from jail. There is a law that says they must register, but many buy homes in residential neighborhoods, and no one ever says a word.

[edit] Steps

Go to http://www.familywatchdog.us.# Look for "step 2" on the site.
Type in your address. The website will then show all the registered sex offenders in your area. (Click on the colored dots for more information about each offender.)
Read about their offense. If it's something serious like rape or child molestation worry. If it's something stupid like indescent exposure the person isn't dangerous, and probably isn't a rapist or predator. If it's statuatory rape look into it more and find out how old they were vs. how old the 'victim' was. If they were close in age it was most likely consentual sex in a teenage couple and they are unlikely to be a pedophile or predator, but talk to them just in case.
This is serious business- if there are any dangerous sex offenders near your address, keep children away from their houses and yards!

[edit] Warnings

Teach children that if anyone makes them physically uncomfortable they should run, and tell a trusted adult immediately!
It's also important that you teach your children to react loudly to any touching that they're uncomfortable with- it draws attention to the scene, and may deter a sexual predator.
Don't ostracize someone because they decided to go streaking one time. Those people are a clear indication of why sex offender laws need reform. These people need your support. Find out what you can do to get the laws changed.