When I wrote "The bus from Liberia...." I was referring to the public bus. There is a storage compartment underneath the bus for your luggage. Bring a day pack (with small children, I know you will!) and put your valuables in it. Keep it with you - don't put it in the overhead bin.
I don't think you will have any problems with someone walking off with your luggage from the storage compartment, but just to be safe - bring a small bicycle lock so you can lock them together.
The bus will probably cost less than $10 for all of you. Kids under the age of 3 (I think) don't have to pay.
Costa Rica is a very "kid-friendly" country. Children are very important to Costa Ricans and they will be kind and helpful to you and your children. You will probably meet other families on the bus.
I haven't seen the new terminal in Liberia but many people have written about how very expensive food and drink is there. If you really need to take a break and have something to eat for everyone, I would recommend taking a taxi to the nearby restaurant La Choza de Laurel. Very good food and reasonable - about 1 mile from the entrance to the airport. You can ask there for the nearest bus stop or just take a taxi back to the airport for the bus stop there.
Edited: 12 years ago