Here are my suggestions...
Break your ritual up into short segments.
Keep segments and the overall ritual on the short side. Incorporate movement and music but don't have too many stimuli at once or it makes it harder for the children to focus.
Give each of them a job and responsibility in the ritual. For example each child could be responsible for calling one of the elements. You might not want to let the child with control issues be in the south (might be a goal she can work up to).
Let the kids give ideas for things to include.
Let them write what they will say to call the elements, etc.
The use of a talking stick is sometimes helpful to remind them when it's okay to talk.
Make sure the "cakes and ale" is something they enjoy and it's even better if they helped to make it.
The keys to success are having a clear structure (this will happen, then this, etc.), get the kids as active as possible, have realistic expectations of them, tailor the ritual to them not the other way around, and above all it should be fun. The Goddess laughs and she's not going to care if little Johny does something right on cue or not.
You might also use positive reinforcement. Make sure to give them praise during the ritual for good conduct. If little Jilly normally can't sit still and you see she's sitting still for a full minute, make sure to praise her. You don't have to disrupt the ritual to do this, a simple wink, thumbs up, or smile can go along way. Also you can have them work towards a goal. For every ritual segment they get through without having to be redirected they get a star. Once they've attained so many stars maybe they get to help lead a ritual or maybe the group of you can make something to present to them for their achievement. That's what I've got off the top of my head.