When Leif started playing Roblox, he began asking for robux - the game's currency - that allows players to upgrade their character or buy virtual items. So his grandparents gave him $200 (£159) Apple credit for Christmas.

"To my shock, he spent all of it in a matter of days," says Ms Ward. "After that, I gave him no more than $10 worth of robux per month. He quickly became frustrated and bored with the game."

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