I have two kids (9,7) and we have done all the character meals at least once during our trips to DLR. My suggestion is, especially if your kids are not buffet-eaters, to try the Lilo and Stitch Breakfast at PPH. We love that meal! You can order off the menu, food is good, and it is less crowded than Goofy's. There is much more character interaction for your kids--during our last visit in May, my girls played three games with Lilo etal during our 60 minute visit. At the breakfast, we saw Lilo, Stitch, Minnie, Daisy, Goofy, Chip (or Dale!?!) and one of the princesses (I think it was Cinderella--have to check the photos).
Another meal we like a lot is the Plaza Inn Breakfast. It is soo nice to be directly in the park and then head out to rides after eating. My hubby always runs and gets FP while we are eating! It is a buffet though--my kids never eat a lot but the characters are fun. My advice is to get the earliest seating available. And yes, you can get ressies before the park opens! You walk through the stores on the right side and then the CMs will let you pass the rope to go to the Plaza Inn. It is less hectic during the earlier seatings--the later is gets in the morning, the more negative experiences with the characters! We have been there when people who didn't pay for the breakfast have come in and commandeered a table! We have seen numerous characters at the Plaza--in fact, usually my girls get enough characters in that we don't wait in line the rest of the day!
I think the only other non-breakfast meal is Goofy's at the DLH. Since it has a mixture of characters, it would probably be most suitable for your 2 kids. 
