For my kids can I go to a family medicine doctor or better to see a pediatrician?

Either Way. It really all depends on preference and your level of comfort. My wife is a pediatrician and I am a family doc and we both agree that for otherwise healthy kids with the occasional illness a family doc is fine. However, i would seek pediatric care if any of your children have rare disorders or conditions as a pediatrician is more likely to have treated these during their training and practice.
Depends. If you are located in a town with available pediatricians that completed their 3-5 year training in pediatrics & keep up with changes in that area, they will have a better chance of recognizing normal variations than any doctor with less training. This can mean fewer tests or trips to consultants for simple issues. Some fm drs keep up and have broad experience with kids & would be fine.