Your children play games and more more that games request the users to pay for more content. But most of time, the gamer are children. Are you sure it is legal to request money to children ?
(1) I think most "gamers" are not children. Many middle-aged people are into gaming, as well as teens, twenty-somethings, thirty-somethings, etc. My mother-in-law will never pick up an XBOX controller or play cell phone games but she goes to the casino and plays the video slots.
(2) My son is 15 now but since he was under 10 he has played games on Steam, GoG and stores like that. He always asks before buying a game or content -- personally I trust him about that.
(3) I am sure there are laws but they are different from country to country.