What kind of dog would be best for my 3 and 4 year old kids?

My kids want a dog extremely bad. My hang-up is that my son was jumped up on and "nibbled" by a loose puppy in our neighborhood last year. Since then he is petrified in the presence of dogs yet he still gets so excited when he sees pictures or videos of dogs. I'm looking for a breed that is great with kids. I took on a German Sheppard pup this week as a "trial-run" from my friend who is trying to find a home for him. Unfortunately this will be only a trial-run because this adorable pup is a big-time biter! I want my kids to have the love for animals that I was never afforded (I was never allowed to have pets as a kid). Please help me find the right breed so they can know the love of a pet. Thanks in advance!