There will be some displays/activities that your 6-year-old will enjoy, but there will also be some displays that are geared more toward adults. It's a nice mix. When our kids went about three years ago (they were 4 and 6 at the time), it was a fun experience for them.
We went quite a while ago, when DS9 and DS11 were 2 and 4. I think we spent about 1 1/2 hours there, and my four year old who is very musical had fun. There were definitely things he could enjoy.