Avoiding wind against tide will help keep the motion down. As has been said, in summer, the mornings are often quiet. I expect you already know that it's much better to keep the kids
happy than to try to get them to recover after a bad time. So here are a few places to test without pressing too far afield:
Block Island -- Crowded on weekends, but a good place to explore and close to your usual grounds.
Narragansett Bay -- Always a much calmer sea state than either RI Sound or Buzzard's Bay. Lots of variety from Newport
to quiet anchorages
. Small, accessible towns like Bristol or E. Greenwich.
Along Buzzard's Bay you've got a bunch of nice destinations that are covered in the Cruising Guide to the New England
Coast. Cuttyhunk, Hadley's Harbor, Quisset and Red Brook Harbor are nice along the east side. Padanaram (South Dartmouth), Marion and Onset on the west side.
On the north side of the canal, Scituate and Provincetown are a lot closer than Salem and will be less exposed to the swells blocked by Cape Cod. P'town Harbor is gorgeous. The anchorage and beach across from town are not to be missed. We love the craziness of the town itself, but you'll have a lot of 'splainin' to do if your kids are at all observant.
Just north of P'town, you're over Stellwagen Bank which is prime whale watching. Scituate is a good walking around town though without the witches of Salem.