You can change the settings on the iPad so that if you buy a song or app…
iPad Basics Part 17 – Setting a Passcode Lock
If you have a tablet, iPad, smart phone, or iPhone, you should set a passcode to prevent unwanted people accessing your phone or tablet.
On an iPad and iPhone you can set the pass code in the settings. You have to choose a simple passcode (four numbers) or a more complex pass code which can be a word or phrase.