An airplane is an enclosed area and inevitably there is a NEED for tolerance for preferences and needs of others so long as it doesn't infringe onto your own personal physical being.
Inevitably the person next to you may wish to drink a glass of wine or a cocktail and it is their right. If there is a child nearby, it is the drinker's decision whether to offer it to the child. FAs are trained not to serve any alcohol to anyone below 21. this is especially in Y. In fact even on SQ, it has been reported that the FAs are quite strict in questioning the age of the passenger in F. So money isn't any issue.
To ask such a question is akin to asking why should women be onboard any airplane. or why should women be given preferencial treatment over men sometimes. And i have seen it happen onboard.More so especially in Australia where there is a lot of self-important female passengers.