Just got back from a journey from Grenoble to Haute Loire, in family (with a 7 year old on his own bike).
The Grenoble-Valence section of this road is excellent for riding with a full equipment. With lovely view too. The only issue is a part of the section between Vinay and St Hilaire du Rosier that is on a road with lorries and fast driving cars, with poor visibility. It is a bit dangerous with kids.
Otherwise, I recommend this route.