We did the Titanic Exhibit as well because DH is interested in all things Titanic. Our kids were 10 and 7 yrs old at the time...the 10 yr old did pretty well and seemed to enjoy it, but my 7 yr old was bored much of the time. I think kids younger than this might have a hard time staying interested. It took us about 1-1/2 hours as well, though you could certainly take longer to read everything in the exhibit. DH really enjoyed it and is looking forward to going again with his mother, though I doubt we'll take the kids through again.
Also, just an FYI, at the beginning of the tour, each person is "given" the name of a certain passenger and at the end of the tour you are able to find out if your passenger survived or not...IMHO, this could be a little difficult for children to understand. It kind of personalized the experience for us, and gave us an interesting perspective on the tragedy.