It seems you have a vacation rental in the area and maybe a car so here's a few things you can do in the area or as day trips from Alajuela as a base:
Zoo Ave in nearby La Garita: not just a Zoo, but a place where animals go for rehab - the bird rehab area is not accessible as they need peace and quiet but the zoo is excellent - very natural settings and the kids will love it
Butterflies - at the butterfly farm in near by La Guacima or at Doka coffee up the hill from Alajuela or at La Paz - all have butterfly gardens
Poas Volcano (45 minutes from Alajuela): leave early by 8am for best viewing - very accesible active Volcano - check out youtube for some recent eruption footage (very infrequent but you never know) and a nice little hike via Botos lake.
Downtown Alajuela: the old museum, the cathedral, the new Juan Santamaria square, the Mercado Central (a typical “experience” in most of Latin America) and on Fridays and Saturdays, the farmers market AKA Plaza Ferias - a real treat if you are interested in Costa Rican fruits, veggies and "culture"
InBioParque in Heredia (35 minutes from Alajuela by car or taxi): this repository of Costa Rica’s biodiversity is also an educational visit contrasting the structure and preservation of the tropical dry forests, the rain forests, etc.
Grecia, Sarchi & Zarcero (30 minutes to 1 hour from Alajuela): wood crafts, souvenirs shopping and photos. Sarchi is home of the painted ox cart; also try the little visited and very nice Elsie Kintzler gardens behind Sarchi (a rare find) and the oxcart factory of the Alfaro brothers - the water wheel that drives all the machinery was rebuilt in 1923. You might even meet the local “Edward Scissorhands” working on the topiaries at the church plaza in Zarcero.
San Jose: city tour of museums, city walk, etc. We like the Gold Museum (world class), also visit the best indigenous art at the NAMU gallery and the newly worked on National Museum, the old Bella Vista Fort.
Doka Coffee: just up the hill from Alajuela (20 minutes). This is the tour of vintage coffee processing using the water separation method for the coffee aficionados. Just show up, they will have space within an hour.
Ark Herb Farm (Heredia area and 30 mins from Alajuela by car). It offers acres of medicinal plants and interesting herbs, unique trees and produce.
Irazu Volcano, Cartago ruins and Cathedral, Orosi valley and/or Lankaster Gardens: you seem to have a car so this is an excellent day trip. There is so much to do in this Southeast side of San Jose that you may end up doing 2 day trips to include the delightful Cachi Lake restaurant, the sugar fields of Juan Vinas, the pre-Colombian ruins at Guayabo, and Turialba Volcano (which you can see from a visit to Irazu Volcano).
Berni
Alajuela