Here's the progression I use:
1) Clearhip with no cast (assuming the kid is small enough for it). You want to be able to stand straddling the bar, either on a block or using a trench bar. Have the gymnast push to a hollow front support with the bar on the thighs. Reach down in front of the bar to grab the gymnast's legs and pull them through the freehip motion to clear support.
2) Same thing, but to handstand
3) Introduce the cast entry. This is the most crucial phase, and the one that most coaches, in my opinion, get wrong. The thing that makes a freehip a freehip isn't the push out at the end -- it's the entry. The gymnast must aggressively drop the chest and shoulders back, such that the freehip doesn't come in from above the bar, but rather from behind it.
A good supplementary drill for this is to have them jump to a clearhip from a box. Put a box in front of the bar such that when the gymnast is standing on the box, the bar is at about chest height to her. From here, she should hold the bar, and attempt to hop up and perform a freehip from here. The box should deliberately be short enough that she cannot get her shoulders over the bar before doing the freehip -- this forces a correct entry (assuming the gymnast keeps her arms straight)
4) Assuming the gymnast has a good entry, it should be pretty easy to then spot her up to handstand. If she's struggling to get enough power, go back and look at the entry -- that's always always always the most crucial part.