I believe a trip to WDW now is just as safe as ever. Believe me, I am no expert on terrorism, but it seems to me that the element of a surprise attact when no one is expecting it seems to be more their style. With all the publicity about Disney, flight restrictions, etc., it seems to me that an unknown target would have less security, and easier to strike. I am a little more worried about this new respiratory virus than terrorism at the moment.
I hope you have a wonderful, safe trip with your family!