We were at Vero last year from March 11 through the 15th. The turtles are not nesting this time of year, unfortunately. There were some existing nests with flags on them on the beach, but no turtles to be seen. However, there are activities all day long for different age groups.
The 6 kids in our group ranged in age from 3 to 13 and they all had a ball. The ocean was cool, but fine for us New Englanders. The only problem was Vero was feeling the remnants of a Northeast winter storm and there were very strong riptides, so we stayed near the shore. The pool was great - we typically spent a few hours on the beach each day and then headed to the pool for the afternoon.
Some of the free activities the kids participated in included the Unbirthday Party, Bubble Time, Chalk Art, Basketball, Soccer, Mini Golf (I think this costs $1 per person now), renting movies, etc. For a small fee they also rented bikes, rented waveboards, and did the Cell Painting class. They were so busy, they never even got the chance to try some of the pricier activities like the Manatee Tour.
We are all heading back in July and everyone is so exited!