Debra,
Even though your plans do not get to take advantage of many Extra Magic Hours, these perks are not the end-all-be-all of a Walt Disney World vacation. When you are traveling with such young grand kids, this is even more true, as these hours get to be harder to take advantage of.
So I would keep things as-is. I love the order that you visit the parks, and especially like your share of time in the Magic Kingdom, which will have the greatest appeal to the kids.
The Chef Mickey's birthday is also going to be very special. Consider a
special cake that you can pre-order to the big meal!
Also, you should know that Downtown Disney does not really get very active until at least 11 am, really more so in the early afternoon. So I would plan some resort pool time on the 7th before lunch at Downtown Disney, some shopping, and maybe a sundae at Ghiradelli's before ending your wonderful vacation!
Have a magical vacation!