I guess it's balancing the boating with the family side.
If we're looking at South Devon and want decent beach / play area with parking / easy access for families with some facilities, also within reasonable range of launch sites and ability to park the boats.
Maybe work back from the family / beach bit.
How about Elberry Cove or Broadsands in Torbay?
A range of launch sites from Exmouth-Teignmouth-Torquay-Brixham Dartmouth.
Easy access from main roads, good parking / beaches, good anchoring for ribs, variety of launch points dependent on how long a trip you wish to make.
Alternatively East Portlebury or South Sands Salcolmbe - bit more of a car journey from the easterly launch sites, and 20nm from Plymouth.
Member of the Macmillan Round the Isle of Wight Club