Windsor Jambs in Windsor SF might offer a 5 year old an interesting look at a dramatic little river canyon for modest effort.
I find an enjoyable and likely educational walk, especially for a child for whom the experience would seem especially appealing, to be at Audubon Sanctuaries where I like to stretch my legs (they don't seem to be stretching but I enjoy the walk anyway) by redlining the trails. Pleasant Valley in Lenox is one such place with a loop of at least 3 miles, depending on your route, which features the summit of Lenox Mtn. and as good of views as you can expect in most of the Berkshires.
A child might enjoy a search for quartz outcroppings and perhaps a souvenir for the pocket or the garden and I guess I think like a child because I look for it along the trails. Though not part of trails I'm familiar with but off of a couple roads in the neighborhood of Greylock and paddling put-ins on the Housatonic River are limestone quarry tailings. Here I've found some nice lime stones to place strategically, near lilacs and lavender, in my otherwise acidic home gardens ... as a reminder to raise the alkalinity for those plants. (Adjusting acidity and alkalinity for many cultivars of hydrangea will also effect the colors of the flowers ... I think of it like litmus paper ... but I digress.)
As for a more challenging hike with some interest in terms of views, a mountain pond and the previously mentioned Sages Ravine, I like a loop which can be done from either the east (Rt. 7) or the west, which I prefer because a loop would entail a mostly gravel road walk. My route starts at Northwest Cabin on the CT/MA state line up Sages Ravine to the AT, north over Mt. Race and Mt. Everett and down along Guilder Pond. There are shorter options available from rt. 7 but the road walk is along a busy highway.
The excitement, and perhaps a cool dip, at Bash Bish Falls is not to be missed. Yes, there can be mosquitoes but I'd say you can't really expect to be in the best of the outdoors without encountering some sort of annoyance so learn early on how to manage them.