What to do after you lost restriction code on the iPad?
What amaksoud said is true. I have the original iPad on 4.3.1 and after trying other advice decided to "read" the com.apple.springboard.plist. 

Here's how to do it and no need to jailbreak. 

Download iFunBox; it's free and works for OS X and Windows. Choose Raw File System and navigate to var/mobile/Library/Preferences. Select the file named com.apple.springboard.plist and choose copy to Mac (in my case). Copy the file to your preferred location. 

Then in Finder you select the com.apple.springboard.plist (that you just copied to your Mac) and look for &lt;key&gt;SBParentalControlsPIN&lt;/key&gt;. The 4 numbers located between the tag &lt;string&gt; &lt;/string&gt; are your Restriction passcode.

For example &lt;string&gt;1234&lt;/string&gt; means your passcode is 1234.

Hope this helps.