Can I picnic or walk a dog here, not just use the bathroom?
Yes, there's a picnic area alongside the restrooms, and it's a normal stop for a short leg-stretch or dog break on the northbound side of I-95.
Can I bring my dog to Mansfield Welcome Center Rest Area?
Mansfield requires dogs to be on a leash or lead no more than six feet long and under the handler's control whenever off the owner's property, which applies on town parks and conservation land.