The boys are travelling to San Francisco to compete against the top players in the world.
Cards valued at about £4,000 were taken after the break-in at a shop in Gainsborough.
Declan from Portsmouth started playing the trading card game aged eight.
Police are investigating the break-in at Trading Cards Gainsborough in the early hours of Sunday.
It is thought about £4,000-worth of stock was stolen from the shop in Gainsborough.
Michael Steranka, vice president at the mobile game's owner Scopely, says it has always been about bringing people together.
Growing up, Kyle loved Pokémon — saving his lunch money for a week just to afford a single pack.
Marcus Koh develops a code he hopes will help with battle strategies in the game's US championships.
Organisers say cosplay allows people to present as their favourite characters in a safe space.
