Pocket money / monthly allowance for kids

What is the going monthly or weekly budget for a teenager’s allowance these days? I used to get by with 20 frank and later 50 frank per week but I don’t think that’s gonna cut it in this climate. So parents (and youth) what would be a fair allowance for a 14-15 year old taking into account that we pay for the mobile phone bill, clothes,… the idea is that discretionary expenses like going to the movies, buying a lego set or a game, going to the kermis, or buying a sandwich at school instead of boterhammetjes van thuis would start to come from the allowance instead of just giving them money when these things come up. Many thanks for your feedback.

** Thanks for the valuable input everyone. I like the approach with the years (13 euro when you’re 13 etc). I think we will go for something like that. Have a good weekend!