Capsey, 18, and Kemp, 17, broke into England's full international set-up earlier this year and have both established themselves in the T20I side. They are both likely to be named in the squad for the T20 World Cup which takes place in February, also in South Africa, and England's selectors have opted against picking them in both tournaments, with England also due to play West Indies in the Caribbean in December.
The squad contains two players who won the Hundred with Oval Invincibles this year in Ryana MacDonald-Gay and Sophia Smale, while Hannah Baker (Welsh Fire) and Grace Scrivens (London Spirit) also featured in the tournament.
Richard Bedbrook, the head of England's women's pathways, chaired the selection panel. "It's hugely exciting to name this squad and to think ahead to the opportunity that awaits the players," he said.
"They're a tremendous group of young cricketers with great potential at the beginning of their journeys in the game. They'll all benefit hugely from this experience - on and off the field. It's important to compete at this age-group and it's equally important to continue the process of learning what it takes to progress to the next level. I'm sure we'll take a lot away from the tournament.
"We have the ambition for the next few months to be a significant life moment for all the players and ensure they use it as a springboard towards making an impact in senior regional cricket, and hopefully beyond in years to come.
"The ICC U19 Women's T20 World Cup will provide an exciting platform for the best young players around the world and it will be really exciting to see our players compete against their peers in a global event."
Chris Guest, the Lightning head coach, will lead the squad in South Africa and throughout the preparation period before the tournament, with former England offspinner Laura Marsh (Sunrisers) and Darren Franklin (Central Sparks) acting as assistants.
England will play group games against Zimbabwe, Pakistan and Rwanda from January 15-19, with the top three teams then qualifying for the Super Six stage.
England U19 T20 World Cup squad: Ellie Anderson, Hannah Baker, Josie Groves, Liberty Heap, Niamh Holland, Ryana MacDonald-Gay, Emma Marlow, Charis Pavely, Davina Perrin, Lizzie Scott, Grace Scrivens Sophia Smale, Seren Smale, Alexa Stonehouse, Maddie Ward.
Non-travelling reserves: Emily Churms, Charlotte Lambert, Bethan Miles, Jemima Spence, Mary Taylor.