We just did this two weeks ago. It may be different if a parent is just supervising then they don't need a tray, but they wouldn't let me in without one so I hung back and my son and wife did it.
Now I wish I would have just plunked down the $7 to get in and let them use the fish so I could take pictures. There is no good spot on that side of the pool to take pictures from, but if you have a good zoom lens (200mm+) you could probably do ok from the far side viewing station near the entrance to the underwater viewing area. Where your party is is blocked by hedges, so unless they are first in the group, and get lined up near the exit, you are not likely to get any useful shots from the near side.
Here's a sample of what I could do.
My recommendation is spend the $7 it's one of the best experiences in the park, but be careful, that $7 can quickly turn in to $50 for Dolphins Up Close Tour like it did for us, or worse yet, Discovery Cove.