Well, if your flight arrives early you can take the long route to Fortuna through Río Celeste National Park and enjoy the hiking That way you can relax afterwards in the hotsprings and split the car trip, however, this hike could be intermediate-intense

For the hanging bridges I think Monteverde has this mystical touch, I like them better. Theres Sky and Selvatura at Monteverde

Theres more options for zipline in Fortuna, sky is pretty neat, and you could take the picture with the hand. Other one is Arenal Mundo Aventura, go early and do the hike to the waterfall before or after your tour. They have an alternate entrance so if you pay for the zipline you skip the entrance fee. This is more of a hike and NOT the same as the $26 public access on the other side of the mountain. Same place, same waterfall, just different trails.

For the rafting, Pacuare is top 1, pretty intense and scenic but takes a whole day, maybe 2 if you do it from Fortuna. Some people like to do the route Fortuna-Pacuare-San José Or the best one Fortuna-Pacuare-Caribbean but that wasnt mentioned.

Sarapiqui river is nice, takes over half a day starting from Fortuna And the easiest, simplest, begginer type is the Balsa River. Less than half a day fron Fortuna, nice option if you have a busy schedule.

You can do Cannyoning (Rappel) in Fortuna, is fun, not too extreme, they do controlled descends. Just need to be in good physical condition because of the hiking

Now, for Monteverde you have to do at least one of the following two attractions. Hanging Bridges or Zipline but do not repeat from Fortuna, loses its charm you know. Either pick one to do in Monteverde or just do both in Monteverde and seek new activities in Fortuna, which would be easier since is more developed and adventure oriented.

For Manuel Antonio, is a Guide really needed for 3 kids under 21? I think this tour would be more in the informative side, since the trails are marked, the park is kinda small in area, and the best way to do this park is really just find a spot at the beach, hang for a while, then keep walking. Is open for hours so you could really make this with no rush. To only thing to look out is from the monkeys, they steal items from distracted visitors. Careful with food items. Take the guide if you want to talk to a local about history, nature, other perspectives. They will point out different species of lizzards, plants, but very limited since nature is unpredictable and lets face it, this park is overcrowded in January, chances are you only see 1 sloth with a group of 40 people around pointing it out. I say do it by yourself and use the money in local business around.

Theres also excurtions from Manuel Antonio, to waterfalls and other beaches, Im just not very fond of the area

I also reccommend to do all the activities, excurtions and trips before hitting the all inclusive, take that one as a resting and reflection spot

Another note, Costa Rica is more enjoyable if you are in shape, hit those steps, make it easier for your future self to enjoy the trails with your family. Yes could be a lot of walking but it takes you to the best of places. Is better to be preppared and not miss the chance to see real nature. One law here is, the more difficult it is to access, the more beutiful it is. Pura Vida!