My child enjoys Fortnite Battle Royale. I wanted to buy him Fortnite until he somehow got a free trial for a few days. All the loot boxes really put me off it.
Fortnite is free. The lootboxes, as far as I know, are mostly cosmetic and don’t give an advantage.
But they are inherently addictive (as in, they are meant to be and it is widely known that they are). You generally want to limit children's exposure to addictive things that bring them nothing at all. It's their formative years, after all.