Joe Caunce, 21, and girlfriend Jodie Connolly, 20, of Milton Gardens, will both do a sky dive in Bridlington at the end of the month in aid of the three-year-old, who was born with a serious brain disorder.
The pair have so far managed to raise £5,000 for Jack, of Hugh Street, Castleford, who is a family friend of Joe.
Joe said: "£5,000 has exceeded our expectations and not bad in just three months – we only decided to do it in November last year."
Joe was part of the Castlefields FC team who climbed the UK's three highest peaks – Scafell Pike, Snowdon and Ben Nevis – for little Jack in April 2006.
Jack's condition has left him unable to walk or talk, almost blind and at one time he had up to 50 epileptic seizures a day.
Joe added: "My girlfriend wanted to raise money for him too so this year we decided together to do a sky dive. Neither of us had ever thought of doing one before now and are really nervous about it."
Jack's mum Anita, of Hugh Street, Castleford, said: "I couldn't believe it when they told me what they were going to do for Jack. I think they're so brave and it's so sweet of them to do something like that."
Anyone wishing to donate to the cause can visit www.jackbrayshaw.co.uk.