There aren't very many coastal roads in Vermont...:W Even along Lake Champlain they're a bit limited.
What size of RV are you taking? Do you have a toad (if applicable)?
Smuggler's notch in Vermont (Route 108 between Stowe and ...) is a wonderful drive and has some fun stops and short (and not so short) hiking trails. Don't try to take your RV over the notch unless perhaps it's a truck camper or maybe a tiny trailer. Large/long vehicles semi-regularly get stuck wedged between the rocks attempting to go through the pass. There is a state park campground on the Stowe side that has a few sites that can accommodate RVs (of moderate size).
Mt. Ascutney state park is nice, too, and the views etc. from the top of the mountain are great if it's clear. There is a road to the top, besides several hiking trails. (The campground is near the base of the mountain.) The top of the mountain really is quite fun to explore.
Camel's Hump is a fine day hike; I usually do it at least a couple of times a year, partly because a trailhead is close to my home. The Huntington (west) side trailhead isn't really accessible to an RV, at least not pleasantly; I'm not sure about the Duxbury side offhand. From the Huntington side, going up and down the Burrows trail is easiest, while making a loop via the Forest City trail, the Long trail, and the Burrows trail is somewhat longer and more challenging but offers some additional lovely views. On a clear day, from the top of Camel's Hump, you can see an incredible panorama: Mt Washington and some of the other presidentials are visible to the east, Lake Champlain to the west (and the mountains of New York beyond), Killington and more to the south (including Ascutney), and Mt Mansfield etc. to the north. This is a quite popular day hike, and certainly within the ability of (many) 9 year olds.