Writing for adults, you have to keep reminding them of what is going on. The poor things have given up using their brains when they read. Children you only need to tell things to once.
I had a bit splurge on reading Wynne Jones last year...and perhaps I could have done with knowing this before my friend and I collaborated on Grimhilda! - we tended to make sure people heard important things at least twice, if not three times. But then it may be different in the theatre, where important points can be lost amongst all the hurly burly.