Both are solid options for families who want a lot of activities and Nicaragua is definitely better when your kids are older, like yours. The logistics require a little more planning and it can feel more culturally immersive since their tourism industry isn't what Costa Rica's is. Roads can be a little rough so I would suggest hiring a driver vs renting a vehicle. It's great for hiking, horseback riding, volcano hikes, surfing and kayaking. I'd check out Rancho Santana, Morgans Rock, Mukul Resort and Yamaya Reefs. Those will be the most on par resorts to what you could expect in Costa Rica. Money will go further in Nicaragua for sure. Of those, I've done the most work with Rancho Santana, excellent property!
In terms of timing, both will work well. Dry season on the pacific side of the country and 7-10 days is enough time to see a couple places.
For a first time international family trip (outside of London) I might still put Costa Rica ahead of Nicaragua if I was giving a recommendation.
Feel free to reach out if you have any questions or want some help with the trip!
Luxury & Adventure Family Travel Agent
Personal Travel Concierge
Europe • Africa • S. America
www.voce-travel.com
Kyle.regitz@fora.travel