Earlier quoted context omitted.
Out of curiosity (I have 2 that are into it) what did they 'get' by you relenting and allowing them to spend Robux? Is it just cosmetics or are there certain games/modes/experiences that are only available if you pay?
Some of it is relatively benign cosmetic items for your avatar, like Fortnite. There is definitely a stigma associated with having "bacon hair" which is the default. Or the ability to play on a server with just your friends. Other times it is a shortcut to stuff that you could get by grinding. $5 gets you twice the XP (experience points) so you can unlock new weapons, levels, etc. Individual games sometimes take this…
https://www.roblox.com/catalog?Category=11&Subcategory=20&Cu...
https://www.roblox.com/catalog?Category=4&Subcategory=37&Cur...
Also you can just go bald for a LEGO-like look, which has always been my favorite.