We did this in August of 2002. My children had a very hard time. If you can, try to find out if it will be high tide at the time you are going.
I say this because the dolphin encounter is in the ocean, on a platform and the small children have life vests on. If their feet can't reach the platform (because of high tide), then they are being hit with waves and banging into eachother and you.
Also, we tried to hold them up, but their vest kept riding high on them. They were not comfortable. My children were 6 and 4 at the time, and they are not small for their age, they are among the tallest in the their classes.
It did help that we were the last people to go into the section, so that when my children got tired of being pushed back and forth by the waves, that they were able to sit on the stairs that leads down to the platform.
Also, you cannot lean on anything, as the platform juts up against a chain link fence (this is how they have them sectioned off).
I personally would not do it again until my children were 10 and 8 so they would definately be tall enough to compensate for high tide. The salt water in the face was not conducive to a relaxing dolphin encounter and at that age, it was a little scary for them.
The dolphins are beauftiful, but the access to them is limited. My children actually go to touch a dolphin more at Seaworld.
So, if you are interested, I would see if you could find out if it will be low tide or high tide that date and time.
Sorry to be such a bummer, but it was a very expensive excursion!