How about you be a parent? Huh?
First off, give them full freedom. And, if that doesn't work, here's a simple solution…
At the end of the night, take your kid's controllers / game devices and lock them away. Then, the next day, the ticket to buy their gaming gear back for the evening is their finished homework that you inspect. Finished homework equals golden ticket to game land. And, during the summer, you give them controllers for x amount of hours a day. Your kid acted like a douche in the store today (even after repeat warnings), then no games tonight. Simple.