For perspective I often have my son with me at fish nerd events because I don't have sitters (and he's three)...
I've brought my son before to this and other conferences. My recommendation is to do like Denise is suggesting and bring the kids and pay for them to enter the aquarium, but not the conference, unless you plan to have them participate in conference events. The lectures are meant to be quiet lectures, like school in a way, and may not be interesting to younger kids. Having brought a 3 year old to lectures and workshops, I can say that unless you child is truly interested in the lecture, you will enjoy it more (and so will your child) if you bring someone else to the aquarium to bring your children around to the exhibits while you attend the lecture.
As for the dinner, I have not seen children at the dinner; it tends to be casual, but not really kid-oriented. If you have to bring your child do so, but again I wouldn't recommend it.
"Kids" that are aquarists in their own right, or learning and would enjoy the talks, are a different case. The club has a long history of supporting and mentoring young aquarists, and those kids I think would have a great time, especially at the workshops.
Christine