On our one and only trip to Kennedy Space Center, our kids were those exact ages. 7 year old daughter, and 5 year old son. We had a great day. I was more worried that I would be bored, not the kids. My husband rarely gives any input in planning our Disney trips, he knows this is my thing and LOVE planning. But he was adamant on going to the Space Center so we all went for daddy to have HIS day. I was amazed and happy we went. However, it isn't an all day thing. If I had the choice back then, I would surely have chosen Sea World over it. We just returned from Sea World in CA and didn't leave the park until closing. From what I hear, Sea World in Orlando blows the CA park away. Either way, I hope you have FUN!!!
Take care