The competition in the city of Hodmezovasarhely starts on Wednesday (June 6) and runs through to Sunday (June 10).
Stephens and Fannon are now experienced on the international scene having competed at last year’s European Games and World Junior Championships and this year’s European Senior Championships.
They form part of a 26-swimmer British squad.
British Swimming’s head of performance pathway Tim Jones said: “We’ve some good experience in the team including proven medallists at European Junior level.
“It will be the largest team we have taken to these Championships in recent years.
He added: “We’re looking to be able to identify a group of talented junior athletes that we can take with us in the coming years to senior success.
“This competition isn’t an end in itself; it’s a significant event but only in the context of being the start of a longer term journey for these exciting young athletes.
“We will be looking to embed some of the athlete and team behaviours that we know we need to see in the next generation of successful world and Olympic athletes.”