The manuals are created in such a way that you are supposed to be able to move right into the next one when you complete the one you're in. However, I know there are concerns about age and maturity sometimes (myself included).
You could slow down a bit, so that you wouldn't finish LHFHG until around June. Then, take the summer off, and start Beyond in the fall of 2009. This would allow both of your dc to mature a bit and be more ready for the material in Beyond. Or, you could continue with you older dd in LHFHG, planning to move right into Beyond when you're done, but keep your younger dd moving at a slower pace, and begin Beyond with her when she's six? I know it gets complicated, but these are my suggestions for now. I only have one young one...the other two will be combined in Bigger...so I'm not sure how it would work. I know you'll get suggestions from others as well.
