While planning your trip, make sure you read about the rides and events and then decide if they are right for your kids.
Each child is different, and you know them best.
When you evaluate a ride or event, make sure you take the "scare factor" into account.
What I found with our son was that he didn't like the 3D movies. Even the ones geared towards kids (I had seen them before, and thought they were cute, and he would love them). I was wrong. He didn't like the dark theater and the load noises.
Another thing I found was that my daughter was OK with some characters, but not others. She wanted nothing to do with getting her picture taken with a 6 foot tall "miss piggy" at MGM Studios.
Also, your two children might like or dislike different things. I found a big difference between those ages. My two kids are 15 months apart. We were at WDW when my DS and DD were about the same ages as your kids. My son went on "Snow Whites scary adventure". My daughter said she wanted to, but when we got to the loading area, my DW went on with my son, and I walk out with my DD.
If you do your homework and plan well, everyone in your family will have a great time.