Check out New England Camper's webpage. He has many reviews of campgrounds in New England.
http://members.aol.com/~newenglandcamper/camping.html
Also, check out Family Camping in New England webapge at:
http://users.rcn.com/buddha/
I would echo Bill's recommendation about starting north and working your way south.
The Green Mountains of Vermont, the White Mountians of New Hampshire, and western Maine will peak about the same time. Western Massachusetts will peak shortly after that. But I would highly recommended the White Mountains. A nice leaf peeping route for the White Mountains is to start in Franconia Notch to Route 302 east, thru Crawford Notch, to Bartlett, thru Bear Notch via Bear Notch Rd. and west on Rte 112 the Kancamagus Highway. The Lake Winnipesauke region of NH is also very nice.
I just drove thru Lost River Valley Campground in Woodstock, NH last weekend and it looked very nice. I will be staying there next week. Their webpage is at:
http://www.lostriver.com/
In the Twin Mountain area, Beech Hill Campground is nice. Their webage is at:
http://www.beechhill.com/
In the Lake Winnipesauke region, I like Meredith Woods. Their webpage is at:
http://www.meredithwoods.com/
As Bill already stated, it can get very cold here in the fall. I usually carry a small electric heater as back up to the propane heater. It could be a mighty cold night if your heater should fail.