You guys should each have your own account. Then you wouldn't have to worry about it.
Just as the above poster mentioned:
Settings> Store> Under "Automatic Downloads" toggle Music and apps off. should be done on all phones.
You can also make an Apple ID without a debit/credit specifically for downloading free purchases if your worried about your kids buying things with your debit card. YouTube it. Pretty easy.
If one of your family members wants to download an app that you already bought (and that's okay w/ you.lol), they can just go to Settings> Store> tap the email address, and tap "Sign Out" then tap "Sign In" and they can sign in w/ whatever account they choose, provided they know the password. Then do the same thing to sign back into there own account after they downloaded the app.
You can also sign in/out of your Apple ID in the App Store. When you Open the App Store, tap the "Featured" tab on the bottom of the screen, then scroll the whole way to the bottom of that page, and the email address of the account in which the iPhone is signed into will be there. has the same functionality as in Settings> Store. Tap the address to sign in/out.
Same way in the iTunes app too.