We have grandkids in your same age range with their first trip to WDW coming up in May. You might show the kids some YouTube videos of the various rides and see what their interests are. Do the kids like characters and princesses? If so, you might get FP for some meet and greets. We decided to splurge on Early Morning Magic so that one morning we can ride unlimited 7 Dwarfs Mine Train, Winnie the Pooh and Peter Pan. I have not idea if they will like 7DMT or not but I think they will like the other two. There is a great thread with lots of info on EMM here:
https://www.disboards.com/threads/t...syland-early-morning-magic-faqs-more.3651152/
Besides that, it helped me to divide up MK by lands. We also won't spend full park days there but we will have 4 days for MK. So on the EMM day, we will just stick to Fantasyland except for a quick side trip to Tomorrowland for a FP on Buzz Lightyear since we have a little super-fan. On another day we will focus on Adventureland and Frontierland and on another day Liberty Square and Tomorrowland and favorites on day 4 (though I will still make FP to guess in advance what they will like).
We plan to FP Enchanted Tales with Belle and Talking Mickey as our only character meets since we are doing a couple character breakfasts.
According to Touring Plans, MK attractions that often need FP are: Peter Pan, 7 Dwarfs Train, Big Thunder Mtn RR, Spalsh Mtn, Enchanted Tales w/Belle, Pirates, Jungle, Space Mtn, Haunted Mansion, Buzz Lightyear. Some of these our kids would like and others not so sure (like Haunted Mansion) but that's where some YouTube previews could help in our decisions.
At 30 days out, you probably won't see 7 Dwarfs FP but you may very well get a FP day of. I have an AP so I can look at 30 days out now and for MK on Feb. 9 the only rides not available for FP are 7DMT and Enchanted Tales with Belle. But those will reload for Feb. 10 within the hour so I would expect Belle to pop back up as available for the new day, but probably not 7DMT.