Not sure if any of these drills are really different then normal but I will throw them out there:
Choose an arm position for all the drills, something simple- I do hands on shoulders. Change arm position once the leap is a little better, then they don't have to think about so much.
Hanging on either a high bar or in cross support on p-bars, lift legs up into split and down quick, add a dyna band tied to ankles once they get good.
Standing back to a hip height mat, lift one leg up onto mat straight behind with just top of foot on the mat. Relax and then squeeze knee. Once they have figured that out, keep leg squeezed the whole time and do small back kicks lifting higher than the mat without bending (start with a lower mat if you need to.)
Stand facing padded wall (I toss a cheese mat standing up against wall), hands on shoulder lift knee up and kick it up the wall. To mimic the develope in a split leap.
Step to split leap next to porta pit, land in splits on the porta pit. Try to hit split before hitting the mat.
If you had a problem leaping onto a mat, try going off of a box or panel mat. It gives them more time to think about it, just make sure they are prepared for the landing. I have seen a lot of kids face plant on the first one, due to unexpected time.
This is all I can think of right now, I will try to add more drills if I think of any.