You don't need to be able to do the splits to do a straddle jump (toe touch.) You do need a degree of flexibility but you also need strength, power and technique. Flexibility is quite rarely the limiting factor. It tends to be an issue more for people who already can do a prety good straddle jump but want to improve it by getting it wider.
Technique wise you need to pick a spot in front of you to watch, jump up, and then snap into the straddle shapes and back out. To improve power try doing repeated tuck jumps on a soft squishy, not springy surface. This makes it harder to jump and therefore forces you to improve power. Punch drills will also help. (Look up gymnastics punch drills.) To improve technique make sure you look forwards and up a little. Try jumping up onto a raised surface to force you to jump upwards (rather than leaning forwards as is a common mistake in straddle jump.) Also try doing pike jumps. These are harder than piked straddle (which is what you want to learn) but because of this again it pushes you to improve your technique and strength in your hip flexors. If they are too hard start with hitch kicks or scissor kicks, jumping and bringing up one leg then the other in front and reaching for your toes. Then more on to pike jumps. Practising pike jumps which make piked straddle much easier when you go back to it.
You may also want to work on improving the strength of your hip flexors y doing V-sits and/or leg lifts. To start you can do leg lifts from a seated position leaining back on your elbows. You can make it harder by adding ankle weights. The best exercise is hanging leg lifts using something like a door mounted pull up bar, but those are hard so you would need the easier version to start off with.
As far as stretching is concerned the prime stretch for a straddle jump is japana. This is where you sit in a straddle and lean forwards with a straight back to try to get your chest on the floor without letting your knees roll in. For a cheer toe touch or trampolining straddle jump put your arms sideways and reach for your feet. So you are doing the same position you are trying to achieve in the air.
With all stretches you need to warm up first (those jump drills will do that nicely.) You need to stretch in a gradual controlled way that challenges your range of motion in a way that encourages your muscles to adapt. Forcing can cause inury (which makes you less flexible) and does not encourage your muscles to accomodate the increased range of motion. You might start with preliminary stretches and build up to japana in a stretching routine, particularly if your current flexibility is not good. Start with a butterfly stretch where your soles are together and lean forwards as far as you can. Then sit in straddle and bend one leg in so the sole of your foot points towards the middle. Turn towards your extended leg and reach for your foot, first with pointed foot, then flexed. Then facing forwards lean sideways and reach over the top for your foot with your opposite hand, first with pointed foot and then flexed. Repeat on the other side. You might then do this in a full straddle or you might move to the full straddle version instead as your flexibility improves. Then you would do japana. If you wanted to learn box splits you would stretch that next, though it is not necessary in order to learn a straddle jump.
All stretches should be held at the point of discomfort, not pain, until you relax into the stretch (usually aboout 30 seconds.) You can push a bit further and repeat but diminishing returns make more then two or three cycles pointless.
P.S. Long legs makes it easier for you to improve your splits flexibility because of the greater leverage acting on the joint but conversely makes it harder to use that flexibility in moves like a straddle jumps beacuse there the leverage acts against you.
Stretch every day, unless you feel excessive pain while you're stretching and after you're stretching. Oversplits are really good for getting splits down, stack some pillows and put your front foot on them. Make sure you're fully warmed up before you stretch. For pike, stand on something 6 inches off the ground or so and reach for the ground, don't bend your knees. For back, stand facing away from a wall and arch back to it and try to walk your hands down and your feet closer. For straddle, put your feet up on both sides and stretch forward. Hold each stretch for at least 30 seconds! :)
STRETCH EVERYDAY. make a schedule and stretching routine. this will help keep you on track and focused. what i do to try to not lose faith is i take a picture of my split everyday, so that way i can see if im improving or not. as for what stretches to do, look on youtube for split stretching videos. if you really wanted to, you could go to your local cheer/dance/gymnastics gym and take a stretching class. im sure youll do great! good luck!
get someone to push you to the point that you are *this* close to tearing a muscle, you need to do it very day tho
