I'm almost afraid to post on this thread?
I will, however, just to say that there is no judgement from me either. My daughter did something similar many years ago. I can't remember the detail, but it was in the days when you couldn't get a cap put on phone account spending, and her phone had to be registered to me because she was under 18. She managed to run up enormous bills three months in a row, after which I gave her phone contract to my husband and got her a PAYG.
I most certainly did have words with her on the subject? I'm sure that she didn't realise how much she was spending, but as she'd been told not to spend anything (at the time I knew what she was doing - I've just forgotten now), I was furious.
It's not the same thing as deliberately taking money, but they do need to know that it matters, both for the account holder's sanity and so that they learn that clicks can cost - forgetting that can be the downfall of adults, too.
I realise (and did at the time) that it was my fault for letting her have a phone with a contract, but that didn't make me any less cross with the little blighter at the time!
I had to write it off to experience, Shinamae, which is all you can do; but don't feel bad about it.