I have a beginner mountain biker wife, 6 and 10 year olds on the trails out there, so I have a pretty good idea. Though everyone's ability and aggressiveness varies.
Easiest routes:
If coming from CR III parking lot: beginner downhill to the Mayors Meander to Connector. Stay on Veritas in the Expert Woods and Connector again in reverse to CR III.
From CamRock Sport in Cambridge. Ride to bridge. Stay on the Connector or Veritas and you will be fine.
All of the trails are also marked on the maps according to ability. Markings are the same as ski areas, green for beginner, blue for intermediate, black for expert. Follow that and you will be OK.
That being said, my 6 and 10 year olds ride all the trails in the park except Cliff Edge. My wife prefers the Connector but is working up to Gettin' Started and Rattlesnake.