We went in oct the weather was decidely dodgy though and we had no dcs but had we it might have been a pain in the rain as it were. loved boston, loved dennisport and particularly enjoyed travelling around rather than staying in one place. check out accuweather website to see what the temps are and decide if its ok for you.
Burlington is cute and you can take a ferry over to Plattsburgh and then drive to Lake Placid (bunch of outdoor sporty things to do) or you could drive north a couple of hours and have lunch/overnight in Montreal plus you have to have icecream when you are there
"Not that much for children imo unless they like beaches,coast,trees.Lovely scenery but there is no Disney etc"
Children's holidays don't all have to be about beaches, Disney and theme parks. I don't understand why parents think that holidays have to be all about what the children want and not about what the adults want as well. There are loads of things to see and do in New England that will appeal to children.
The Science Museum in Boston is also worth a look - lots and lots to do and see there, for all ages. You don't have to spring for the Imax theater or planetarium shows to get a good day out.
There are also Duck Tours in cities like Boston and Hyannis which I hear are fun. My in-laws went on one and had a good time.
Check the weather channel for temps and weather - will give you an idea of what conditions are like just now. Sometimes it's warm and sunny, but sometimes it's rainy, like this week.
Going in October it will be cold, but colorful and New England loves Halloween. In addition to city stuff, the suburbs and countryside usually have things going on like hayrides, apple picking and I think corn mazes around that time. Just be warned that some of the hayrides and corn mazes are put on as "haunted" and those can be properly scary - might be a bit too much for your kids to take, depending on how active their imaginations are (my DSD had nightmares for years after watching The Wizard of Oz...).