Sample of things kids who play Fortnite have (indirect) decision authority on:

fortnite v-bucks default gift for birthdays, displacing the movie gift cards

racking up hundreds of dollars worth of v-bucks per year

getting family to buy a Samsumg S10+ so they can reap the associated "skin" to their Fortnite account

graphics cards upgrades

(expensive) gaming mice and other gear pushed by youtubers

general merch like toys