PIN coding airplane mode iPhone

Has anyone else had the same problem as me? My wife and I used to let our son, who is just about to turn 3, play games on our iphones, with airplane mode engaged. Unfortunately, the little monkey has learnt how to turn it off, resulting in a 7 minute call to one of our friends answerphones, who found it funnier than the emergency services would have done...
Can I suggest to anyone from Apple who is reading that an option to PIN code airplane mode be considered for the next upgrade of the OS? Any thoughts, or supporting posts?
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