Wow eph2-8 I don't know where in Costa Rica you went but that was nothing like my experience.
I found Costa Rica to be one of the safest countries I have travelled to. However, like anywhere you should always be on guard and never stray in to areas where you likely shouldn't. Basically use a little common sense.
We were in Liberia/Tamarindo area. We did have a car but you certainly don't need one. Lots of buses and cabs and they are very reasonable. Never saw any pigs, cows or donkeys on the road but did see a sloth slowly (very slowly) crossing the road. Some of the roads/highways weren't in ideal condition but nothing crazy.
The local "Tico" restaurants are referred to as Soads and they were some of the best places we found and CHEAP! Beaches were nice but you really need to do a little research on the best ones, most of the public ones were pretty standard. If you like to surf there are lots of great spots.
We took both our kids they were 10 and 12 at the time and they really enjoyed it. We were not at a resort and had a rented a condo on VRBO. The kids made friends with a few of the local kids that lived in the same complex and were playing and swimming in the pool. I wouldn't hesitate to take the kiddos again. We did a day tour to Eco Adventure place and they got to see monkeys, tucans, sloth, snakes and lots of other critters.
The local currency is Colones, although American money is widely accepted pretty much everywhere. But be aware if you are off the beaten path with only American money you will get your change likely in colones. So good idea to know the exchange rate as they will likely short you a few bucks! Majority of people also spoke English in the more touristy areas, even off the beaten path it wasn't difficult to communicate, there was usually someone that could help you.
So ya I definitely recommend Costa Rica even with kids. There are lots of good sites online to help you plan as well. Go! Have fun, you won't regret it