Television adventurer and the world's chief Scout Bear Grylls has launched a "Summer Manifesto for Children" to encourage them to learn new skills, enjoy outdoors and be more adventurous. In the hope that they will put down their computer gadgets and explore the world around them, Grylls is urging children to do something as simple as spending a night outdoors."School holidays are a massive opportunity for fun, challenge and adventure."That's why I'm challenging every child to accept my manifesto."Grylls practises what he preaches with his children - Jesse, 11, Marmaduke, 9, and Huckleberry, 6.The manifesto includes:Spend a night under stars in garden or camp;Do something for someone else;Get fit by jogging, climbing or cycling;Build a tree house;Go on a wild adventure. ..