Some people find arabians very easy, some find them very hard.
I've always found them to be pretty easy.
There aren't really any particular progressions I'd use other than doing them into a pit or onto a soft mat. One thing I've found pretty helpful is getting a thick stack of mats (I usually use 16" worth of mats for this) and doing arabians on to this. Kids will usually land on their back or butt, but it seems to be pretty effective at getting them comfortable with the skill while keeping them from pulling down on takeoff.
Just make sure the area you have for them to land on is wide. Kids who are just learning arabians almost always go crooked.
I have another question about arabians. What do you think is easier backtuck 1/2 twist or arabians. I can do a 1/2 twist already (working on full twist), so how hard do you think it would be for me to learn an arabian? My club doesn't have a pit or anything to learn them in.
A simple drill for a first step to an arabian is to do A round off rebound with a half turn and then punch front tuck. The half turn (done with a straight body and arms up) comes after the round off and lands on the ground before the punch front tuck. This is a simple aid to get the feel for turning and then accomplishing another skill.