These can be really discouraging if they are introduced suddenly. I like to have kids lay on their backs over a barrel and practice standing up even as they're learning cartwheels just to get used to the movement. Arms straight, squeezing the ears the whole time, etc. The barrel supports weight, but the gymnast has to use her muscles to stand up.
If that's too easy for you, there's another one with the barrel. For a Front Walkover, place your hands in front of the barrel, fingertips touching the bottom of it. As you do the kickover (over the top of the barrel) you're creating momentum, and this is what you want. Where things go wrong usually is not following through with that momentum by actively using your arms. Think of them as not only straight, but pushing against the floor. Obviously since you can't fly this means nothing when your legs are in the air! However when your foot touches the floor, if you aren't pushing through from the shoulder/arms then your momentum dies, the skill stalls, and suddenly you have to muscle your way up to standing rather than follow where your momentum carries you. MUCH harder. It's worth mentioning that the barrel will move forward as you do, don't freak out. It's a sign that you're going in the right direction!
The reverse is to stand with your back to the barrel and do you're back walkover. A common mistake in this drill is to have the arms too far forward in the backbend. If you can see your arms as you stand, they are too far forward. Push them back, and keep that tension as you bend back on the barrel or it will be difficult to support your weight through the kick over. This one should be easier than the front one since you're standing from a hollow rather than an arch through the back, more natural feeling. Still push through the shoulders so that you flow through the skill rather than have an exaggerated push of the hands off the floor as you stand.
I would do those until they become easy, then do them 100 times more. Do them on the wedge as well. If you have a spot, make sure the coach doesn't allow you to stall in the skill. With a spot you want to feel how it goes fluidly, not reinforce how it feels to fight your way through it.