Under age magic - just wondering?

[Andrew]

No: HPFGUIDX 188295

Hello, just wondering what people think about this.  Why did the Dursleys seem totally ignorant of the fact that Harry was not allowed to perform magic outside school until he got his warning letter from the Ministry when Dobby performed magic in the Dursley's kitchen.  At one point Petunia described Lily as "coming home every holiday with her pockets full of frogspawn and turning teacups into rats."  If Lily turned teacups into rats during the holidays surely that would constitute under age magic.  As Lily apparently was not expelled from school I'd imagine that she never, in fact, did such a thing and that Petunia was purely making it up, a case of over exaggeration.   However, as Lily and Petunia would have been living at home during the holidays, I'd have thought Petunia would have been aware of the fact that Lily would not be allowed to do magic out of school.  How come, then, she did not know Harry would also not be able/allowed to do magic during the holidays?  Was it!
  Just because she was so afraid of magic that she never actually took any interest in her sister and how she behaved during the holidays?  Would Lily ever have mentioned the fact she wasn't allowed to do magic?  Was it just the fact that she never did magic out of school and so never received any warnings, meaning Petunia just never knew about it?  Or was she, in fact, being even more devious than most people may think, hoping Harry would do under age magic and then get expelled from Hogwarts (another attempt at trying to stamp the magic out of him).  Personally I'm more inclined to think it was total ignorance of the truth, not taking interest in what Lily said/did during the holidays and so being totally unaware of the fact, but just wonder what others think.

AJM