I PM'd you as well, but this is a good location, where I've stayed multiple times.
There's an excellent river trip available a little bit north, on the Tarcoles River. I've had great success shooting there, with minimal effort since the boat and water are doing most of the work!
Manuel Antonio is definitely worth a stop, and yes a day trip is very do-able.
Lastly, I would look into a stop at Carara National Park. I would do this as early morning as possible, since the heat can get bad late morning or mid-day.
I had forgot to mention a macro lens, and that is certainly a good idea. Many beautiful butterflies, interesting bugs, lizards, flowers/orchids, etc.
Asher - I think that with Don't experience in shooting in Costa Rica, he would be a wonderful resource to access being that he has offered. Enjoy your time and come back with some images that we can view and enjoy. This may be a once in a lifetime adventure for you - so it is good to have a wide range of focal length as has been mentioned - - - example macro, super wide angle to tele and super long tele.
I have personally found that a 600mm or longer tele lens is essential. I don't have the budget for a 600mm f4 nor do I have any interest in hauling around big heavy lenses. One year in Costa Rica I saw a guy with a big 600mm f4 on a pro body mounted to a huge Gitzo tripod - plus a couple of pro bodies with huge wide to normal zooms strapped to his body - - - climbing up and all over Poas volcano area at 9,000ft elevation (it hurt my lungs at times just walking without considering gear) and inclines going up and down 1,000ft for as much as 3 miles. It was crazy to me, and the couple of times I ran into him, he was panting and resting and not taking photographs - while I was taking many in a large variety of situations.
My option has been for the much smaller and lighter 140 to 600mm equivalent Olympus lens. Even with that focal length, many images have to be cropped. Yes it is dark in the jungles and forests, and you will be shooting at a higher ISO setting. Fact is that you aren't going to be having any speed demon for a long lens, regardless how much you spend (f4 is about the fastest for a 600mm). One year my friend used the Sigma 150-500 on a crop sensor Sony DLSR and had a little more reach than my lens - although it was a bigger and bulkier lens.
Personally I can't use a tripod for such shooting. They are bulky unwieldy and most of the time I am coming upon birds or animals where I would miss the photo, if I were to set up on a tripod. As well, I never came across many animals that were sitting right there in front of me. On the other hand - if you have lots of time and are intent on scoping out a few specific birds or animals and can come at different times and somehow get close enough to them - an anchored setup would definitely work.
It will all depend what type of shots you want of course. Playa Hermosa on it's own is kind of interesting - a pretty beach. It may be that off the beaten track, there is some jungle area with animal life and greenery.
As Don has mentioned,
Manuel Antonio will provide some wonderful photos of up to 4 different kinds of monkeys and some smaller ground creatures.
I as well, really recommend
Carara National Park (a little bit east of Jaco) if you and the kids want to be trilled by being close up to tons of wild Crocs. Amazing there also are Scarlet Macaws and a ton of small and unique birds - - - but shooting into the jungle roof does take a long lens. Even just seeing the crocs from the Tarcoles River Bridge, is pretty cool. But if you had the time to go down the Tarcoles River in a boat as Don mentions - would be awesome I'm sure.
I currently find that even shooting with my 300mm focal length is limiting compared to my use of the 600mm. All of these shots below were taken at 600mm focal length. Photos below taken on the beach of Playa Hermosa, could have been shot with a 70-200 - but benefitted from my 140-600mm zoom (35mm equivalent) - mostly near the 600 end with these. Careful though - the longer the lens the more difficulties acquiring good focus - especially when the subjects are closer (shallower DOF).
My photograph of the feeding Red-legged Honeycreepers (male and female) that is being used in a environmental department at a Hawaii University, was taken shooting up into the jungle roof with a 600mm lens, but still required cropping to to the stage. Shows how content, outranks ultimate image quality as they were not able to find other photos of a pair together while eating their favourite fruit. Doing a Google Search, there are many "slick images" of this bird with nice setting and blurred out background - - - but none the way I took them, shooting handheld with my more limited gear:
https://www.google.com/search?q=Red-legged+Honeycreepers&client=safari&rls=en&source=lnms&tbm=isch&sa=X&ei=97xGU4HaMYiysQT574HgDw&ved=0CAgQ_AUoAQ&biw=1436&bih=766
The photo of the Black Igauna, also required a 600mm focal length to capture this skittish creature. Both of these were taken at
Carara National Park.
All above stated - - - my purpose in photographing the scenery and wildlife, may be totally different that yours Asher. I am not shooting as a specialist in any of these areas. I am just someone who loves photography and wants to document my adventures with quality images of a wide range of content. I don't look at them as snapshots, but photographs that can be sold as prints, exhibited, and used in publication if the content is unique enough. But I'm not a pixel peeper or a photographer who has to have a perfectly setup blurred out background suitable only to the perfectionist.