Hello, me again!
We took our girls (5 and 2) on a boat trip this year and like you I wanted to make sure we found a good boat. Some of them are too big and full of 18-30 types, which is not what we wanted, so I got my husband to ask around for the best ones.
We booked along the beach in one of the booths, the one towards the far left facing the sea - near Tropicana and Siesta - with a guy called Tyson. The boat was really nice, not too big with planty of shade. We got there early and got oursleves a table inside, which was perfect for the girls, they could do their drawing and stuff and the littel one could have a sleep in the afternoon.
It cost about £12 each including food and unlimited drinks (local brand soft drinks and beer, but all perfectly drinkable) and the girls were free. We had a great day out, I was a bit worried it would be a bit too long for them 10am til 6pm but they really enjoyed it. i would think at this time of year you wouldn't be out so late though.
Have a great time - I wish I was going back tomorrow instead of being here in rainy London !
Kedi