How can I stop the Android Market from showing bad/naughty apps?
The Android Market has an included content Filter, which should filter most of these Apps. Ratings are


Everyone
Low Maturity
Medium Maturity
High maturity


Android 2.3 and lower


Open Android Market.
Press Menu and touch Settings.
Touch ‘Select filtering level’ and choose your desired setting.
To lock the settings, touch the lock icon and enter a PIN code.


Android 3.0 and higher


Open Android Market.
Press Menu on the upper right corner.
Touch ‘App Content Filter’ and choose your desired setting.
To lock the settings, touch the lock icon and enter a PIN code.


Source