I would definitely not recommend Jack Russles or Boston Terriors. Our experience with those breeds is that they are very high strung. I know two people with Jack Russles and they are really smart, but they are crazy!
Beagles are great family dogs. They are good with kids and really gentle. They are great walking partners and walking them is actually good because they are hunting dogs by nature and need the workout. The down side is that they don't like being left at home, so if you work outside the home or are gone alot they get sad and bay until they get used to it. Other than that they are pretty fabulous.
We had a Lhasa Apsa (sp?) and he was good too. I talked to a breeder and he said they and Shitzu's are very calm and good with kids. Ours was great with our kids. The down side for them is that they have all that hair and you either have to brush them alot or keep them clipped pretty short.
Hope this helps and have fun finding your dog! =)