Your kids are a good age for a busy summer trip, it'll be alright.

Get there at least 15 minutes before the park opens, more if you can handle it. Use your MM as soon as possible during your trip.
Use FP for those rides and ride other popular rides that don't have FP during the morning (Toy Story, Peter Pan, etc.)
Bring lots of water, and maybe one of those spray fans.
Make sure to have some easy snacks on hand and eat regularly to prevent crankiness of all.
Take a break if possible during the middle of the day. Naps if you're tired, or swim time at the hotel pool. The middle of the day is the hottest and most crowded.
Plan your night time entertainment and which park you will start the day at ahead of time, pay attention to things like EMH days that you can't attend, try to go to the other park if possible (except on your own MM day of course.
Have Fun!