When Christian Hosie was first learning to kayak his mother warned: "don't go out too far", but now he and brother, Wesley, are planning to kayak 25 miles across the Channel.

And if they succeed Christian, 13 will be the youngest by three years to make the crossing in a style of vessel originally designed by Eskimo hunters.

The brothers, from Taunton, are aiming to raise money for the Children with Leukaemia charity.

They are already well into a six-month training programme, practising at weekends at Wimbleball lake, high on Exmoor – which during the recent severe weather has been a particularly bracing experience.

They have a one-week weather window to make the crossing – between May 23 and 30. When they take to the water, probably around 5am, they will be using racing kayaks bearing the arms of Taunton Deane, thanks to a plaque presented by mayor of Taunton, Cllr Tim Slattery

Wesley, 19, is a student at Richard Huish College. At 13 he was a member of the GB water-skiing wakeboarding team. Christian, a pupil at Taunton Preparatory School, wanted to follow a similar sport, but fell in love with kayaking on a school trip to France.

Their parents, Bill and Catriona, believe that the sports have been great ways to build their sons' confidence. Mr Hosie, a pilot, is helping to supervise training.

Wesley, who has just returned from working as a ski instructor in Canada, said: "I regard myself as quite fit and spend a lot of time doing sports, but this involves a different muscle group. We have to spend a lot of time paddling to build our muscles and have been using St James Pool, locally, as well as Wimbleball. When we cross the Channel we will be paddling for something like four to six hours."

Christian said: "It is a challenge and will be physically demanding. I am really looking forward to it." From March 1 the pair will be training in open water in Plymouth Sound, and in Poole harbour, to expand their fitness and build stamina.

They will be accompanied on their crossing by an expert support boat seen by millions when it supported BBC's Top Gear presenter, Jeremy Clarkson as he crossed the Channel in a jeep. They also have the support and expertise of Taunton Canoe Club, Poole Harbour Canoe Club and Wimbleball Sailing Club. All their kit, totalling £2,500, has been sponsored by AS Watersports of Exeter.

The route is almost exactly the same as the Channel tunnel, starting and finishing at both the entry and exit points. The boy's will be starting from Shakespeare beach near Dover and will finish at Sangatte. To make a donation visit www.channelcrossing.net