We did two character meals on our last trip with my fiances six year old son. The first was the Princess dinner at Ariel's Grotto. I made the reservations thinking he would think nothing of the Princesses. He loved it.
He was ready to marry Jasmine by the end. The princesses do a fantastic job of interacting with boys as well as girls. The examined his pin collection (Mulan warned him that Jasmine wouldn't like his Jafar pins), Ariel taught him to bow like a gentleman and then Jasmine refused to go near him until he took off his lanyard (the Jafar pins...he loved them).
We also did the Lilo and Stitch breakfast at PPH. If your kids like Lilo and Stitch it is guaranteed to be a hit. Not only did we meet Lilo and Stich, but Minnie, Daisy, Max (Goofy's son) and Goofy. It was a blast! It was a buffet (we hardly ate anything), but Stich made all the money worth it. He came by our table twice and gave me kisses. I so
Stich, he is my favorite!
But if you are unsure, you could always make a priority seating reservation for both and then judge the reactions they have to the characters in the park and then cancel one. Good luck!