If you've never been before, this is a GREAT beach for kids--the beach part is a man-made atoll pool, so it's like a pretty small, shallow lagoon with no waves. The beach is moon-shaped and flat, so you have a good vantage point to watch the kiddies. There are palm trees all over for shade. There is a really basic snack bar, but no chair rentals or anything like that. But the best part is, during the week before school is out for the summer, you practically have the whole beach to yourself. There are always a few other moms there, so your little ones will have other kids to play with, but it's sooooo nice and peaceful and beautiful and laid back.
On the flip side....once summer really kicks in, and it is more crowded with kids all day every day, and the sun is really heating the lagoon water to almost bathwater temp, I stop going there and switch to Key Biscayne, because....ewww! It's like the water is stagnating with all the....well, you know how kids are in the water, with their bodily fluids free flowing and all....it just grosses me out. I mean, this beach is almost ALL littler kids (six and under) and their parents. And I've heard stories from other moms and nannies about their kids getting unexplained rashes, or funguses, and even though unproven, they kind of blame this beach. According to the brochure and website about Matheson Park, the atoll beach is "flushed naturally by the tidal action of nearby Biscayne Bay." That's great to know and all, but I'm not convinced that the "natural tidal action" of Biscayne Bay can necessarily keep up with day in/day out toddler poo and pee-power in the middle of summer.
My point is not to talk you out of this beach right after I talked you into it, but to say GO NOW! before school is out. It's been lightly used for the most part over the winter, it hasn't gotten crowded yet for the summer, and with all the wind we've been having, the water has been circulating like mad. $5 parking fee. There is a marina and some other stuff at Matheson Hammock, so if you're unsure of how to find the beach ask at the guard gate. For more info, check out their website.