I have been 15+ times to Disney world and have probably eaten at Ohana's 8 of the times. It's amazing and has a family atomosphere. They play games with the kids during the meal. Also, don't plan anything for that evening because the meal takes around 2 hours and you will be so full you won't want to do anything afterwards.
My family and I went to Chef Mickeys the year before last and we all agreed it would have been great if we were 5-10. The food is ok, nothing special, but the characters are what make it great for kids. They come around visiting your table every 10 minutes or so. It's great for kids.
Haven't eaten at Sci-Fi since I was little but it was good and I have heard good things.
Let me suggest two places that your should consider. First, Cinderella's Royal Table inside the castle. It's grade for kids, but very pricey. I won't ever do it again because I am too old for that kind of stuff, but being a long time Disney go'er I thought it was cool to eat in the Castle. Also, Planet Hollywood at DownTown Disney is very cool.
Thanks for the feedback. We are very excited to try Ohana for the first time for dinner, it's one of our favorite breakfasts. I am definitely going into Chef Mickey's with low expectations for the food just happy to bring the kiddos to a Character Dinner.
We have done CRT for breakfast and dinner, liked the breakfast a lot more food-wise. We decided to skip this choice on this trip. It is super cool to go into the castle but like you said it's pricey and there is no meal that rushes you in and out of there more. We were considering Planet Hollywood as well but I'm going to still try for TRex first. Thanks again!!