Its cos you are on stilts that raise you off the ground and can help you jump really high.
Or rather you keep THINKING about that fact. You know if you were just on your feet you could jump off a 3 foot wall no probs...but its scary on the stilts. So try and forget you are on the stilts . I bang on about powerball, but it really helps. Even just a game of catch with some1 , with them throwing 'difficult' balls, high, low , to the side. You quickly start to forget you are on the stilts and get much better balance.
If you can get to a gym , try jumping on top of a craSh mat, they are normally 1 m high. Then once good at it pile 1 on top. Then go back down and jump on or over a 1 foot high 'solid' block ( aerobic things are good). Then try going outside and finding low walls and the like to repeat. Some1 to gently push you on will help too.
Jumping off things is, for most people, easier. So do a fair bit of that, then you can say 'yay i can do stuff'. Great if you can find a wall that is horizontal, but in front of ground that gently slopes down (parallel not perpendicular). then you can try jumping off and on and as you gain confidence you can move along with the wall gradually getting higher.
Tho it can be good to be pushed or push oneself, also set realistic goals. This will help avoid the frustrations you are feeling at the moment.
Well 1st lil burst of thought