This is what I have read from other posts. if I am wrong, I'm sure someone will correct me.
Yes it is within walking distance. I think it is either right next to the cruise terminal or across the street.
Yes, they have a spot where they can hold on to your luggage for you. (That's a nice perk)
I read the reviews - some loved it and some said it was not worth it. I guess it depends on your expectations and if your girls have been to something similar. It seems MOST people with younger children tend to like it. I would go if I were you. Lots of interesting things to look at and you can stroll around at a casual pace. Now in my case, I have teen boys. I'm sure they would like it for a short time but I don't think they would like it enough for us to spend the money on it. We are looking for some things to do in Tampa also.
Good luck and have a wonderful time.
Feb 1986 Mardi Gras
Aug 2010 Inspiration
Aug 2012 Paradise
Sept 2013 Valor