Wow, whilst I don't see the point of spending that kind of money on these things at all, I wouldn't expect a parent to stop their son/daughter spending their own hard-earned money on it? I bought stuff that was way more stupid than a class ring with my money when I was 16/17/18 but I earnt the money so I could do what I wanted with it?
I'm another parent who will be stopping their child from spending large amounts of their own money. A few bucks - they can make their own decisions. But large amounts, I'll be involved until they are financially independent. I would highly discourage spending $400 on a ring. Spring break trips won't be happening. Cars, sorry Charlie. If they can convince me they are being smart (like going to Walmart and getting a less expensive ring) - maybe. But to me, it's not just up to them just because it's their own money - because it's my job to help them manage their money.
It makes no sense to me for them to waste all their own money only for me to give them more money. I expect them to be saving money towards college expenses, etc. At 12 and 14, they're saving for that already.
My parents were involved in my finances until I was financially independent. I'll do the same.