My personal preference would be a Pit. I would second that with a Boxer. Pits seem to be both tolerant of the typical children behavior of the tail pulling, ear pulling, eye gouging antics and EXTREMELY protective of them. They're extremely active and live to play. They're also not too big nor too small...just right(my female is a solid 65lbs at 3.5 yrs old). Here's lilly from about a year ago:
...This one should give you a better idea of the size and is from about a month ago.
I haven't owned a boxer myself, but I have had a number of friends over the years that swear by them for their children/family settings. They seem to be extremely tolerant as well...and goofy