If it was me coaching them, my first step is to work out what their twisting direction is. I know some people like kids to just go with instinct, though for me, once they've established the easiest way to do a roundoff or cartwheel that is it. If they cartwheel with their left leg, I teach them to twist left. Right leg, right twist.
I'm assuming if you're considering coaching the front salto 1/2, that they can do a decent front salto?
For adding the twist, I find it easiest to work with a pike instead of a tuck.
So drill 1 - Laying in dish (or hollow if using American terminology), twist to prone hold.
Drill 2 - Laying on their back in a pike, holding onto ankles, snap open and twist into prone hold on floor.
Drill 3 - On trampoline, back drop and 1/2 to feet
Drill 4 - On trampoline, crash dive, 1/2 to feet.
Drill 5 - On trampoline, front pike, jump 1/2.
Drill 6 - Onto a stack of mats, or a soft 90cm box, do a forwards roll into an inverted pike, then snap open with 1/2 twist to land feet on floor. This can also be done with a salto onto their back instead of rolling into position.
From there its just a matter of attempting the front pike 1/2 from a mini-tramp into a pt I'd suggest. I'd aim to make sure they are in an inverted pike like in drill 2 before attempting to initiate the twist.
Advantage of learning to twist using the pike is you teach a late twist, so you don't get them staring at the floor while twisting and getting lost or twisting the wrong way.
Hope that helps?