I'd start with booking your first FP+ at around 10:30 as that's when the waits really become long. I'd do 10:30, 11:30 and then maybe a 1 Pm to leave time for lunch somewhere in there. I'd definitely plan to use the FP+ for can't miss stuff and then I would understand that you will do some waiting for other attractions after that unless you can get a 4th FP+ that suits your needs.
Remember that
if that 4th FP+ isn't scheduled time wise until later at night you will be blocking yourself out of any additional FP+ until that time window opens.... SO you might want to save the 4th FP+ for the first thing available in the afternoon and then try again later for a 5th, 6th etc all while traipsing back and forth to the kiosks to make that additional FP+ reservation.
Keep in mind that you will probably have to stand in line at the FP+ kiosks BUT
that is way less time that you would be standing in line as a standby rider on any attraction during the rush hours so it is actually worth it time wise.
The down side to the 4th FP is that you may very well be getting the dog's breakfast

as far as choices are concerned. Josh from Easy WDW says that during the summer months the 4th FP+ availability for the desirable rides pretty much dries up after 11:30 am. The good news is that with that 4th FP+ you will be cruising past all the other people waiting in line on that ride.
With the age groups that you are touring with, running on to the Dog's Breakfast rides without waiting may be more fun then waiting an hour to go on Pirates or some other must see that you didn't make the cut in the first 3 FP+ choices.
Before you go make sure you know Where the FP+ Kiosks are located and which ones are crowded and which ones have smaller lines. (For example the easily seen Stitch FP kiosk is crowded but the one around the corner at Buzz Light Year is less so.)
Here is a list of the MK FP+ Kiosks:
1.Fantasyland:Storybook Circus in the very back tent near Pete’s Silly Sideshow
2.Adventureland: Jungle Cruise old FASTPASS machines to the left of the entrance
3.Adventureland Breezeway to the right of Diamond Horseshoe, across from Treehouse
4.Fantasyland:To the right of Mickey’s PhilharMagic
5.Tomorrowland:To the left of the Stitch’s Great Escape entrance
6.Tomorrowland:Buzz Lightyear’s old FASTPASS machines to the right of the entrance
7.Main Street:Town Square Theater just inside the entrance on the right
This Kiosk list may change or it may even be incomplete. You will have to keep posted as to all the latest developments because things could change at any minute when it come to Disney.
I'm no genius and I did NOT in fact stay at a Holiday Inn Express last night. I just get all my info from the Easy WDW site
http://www.easywdw.com/ so that's how I am figuring things out, keeping up to date with all the changes and sharpening my touring teeth on all the latest strategies. You'd be well served to do the same with Josh's site.
Here is another link to a page on that site that gives you Disney World Summer Wait Time Trends. It's broken down by each park and then each ride has data for each hour so you can see the rise and fall of wait times at various attractions.
http://www.easywdw.com/uncategorized/disney-world-summer-wait-time-trends-june-3-2014/#more-13581
This will give you an estimate of what your wait times will be like for that ride that you didn't choose for the FP+ but you still have to go on. At least with that information you will be able to plan realistically and not go in to it blindly. These wait times are why I'm thinking that with your young group it may be better to keep moving with that additional 4 FP+, 5th FP+, 6th FP+ etc.... Because really when you think about it there is a lot of stuff, Except for that Stitch attraction that is still good i.e. better than you remembered, and you will walk out of saying you were glad you did that.
(Please Dear God do not even consider going on that Stitch thing as you will never ever be able to get those 20 minutes or so back in your life and the kids will probably get scared!) Still not convinced? then read THIS:
http://allears.net/tp/mk/mk_sge.htm
So that is a lot to think about but also there is a lot of really great information out there on that Easy WDW site to help you make informed choices that will help with touring for your group. Have a great trip and above all, save your money and do not stay at a
Holiday Inn Express because it probably won't help anything you do at WDW.
In case you are wondering what
THAT is about here is a Video showing a person much like yourself cracking the equation for the perfect Disney Touring plan:
http://www.youtube.com/watch?v=7jo_x7ecIFg
~NM