I went with my 6 year old son today, and it was fun. He wanted an adventure on a real ship, so that was a surprise present for him from me, which he felt very excited about. The crew was polite, the ship was clean and well maintained (although the menus were sticky).
The crew members let you help raise the sails which is fun too!
Stuff I would have improved is probably telling the visitors what they see around them, what kind of stuff they sail by. I did my homework and learned about the landmarks, and my son was asking me about every little thing. What's that green thing with the light on top that we are passing by? What's that structure? Why does the water here looks so green and so black? What's that island? And what's that one? How does a ship like that work? Why do we need sails? etc, etc, etc. I was describing all this for him, and I noticed that a few other people wanted to listen to it too. I think that's a great opportunity for making the trip even more entertaining.