I live in Exeter (and have a nearly 4 year old) and would second Ladram (not stayed there but location is good). The beach can get very busy in good weather, but Exmouth and Sidmouth are lovey, Exmouth best for sand, dinosaur play park and other attractions. Sidmouth is stone, but is best for swimming and has a lovely little town.
Darts and Greendale farms (play parks, animals, various eateries and shopping) are close too if the weather isn’t great but dry. There is a lovely walk to a RSPB bird hide from Darts, ours scoots happily too, as she knows there are ice creams there. Check out their Facebook pages for events if that is your thing as well.
We’ve stayed at Ruda recently and its location was fab, you can walk to the beach and into a little town. Reasonable pool, soft play in the restaurant, entertainment (some free, some paid for) on site. DD loved the Paw Patrol entertainment 🤦♀️
We have done Salcombe/Dartmouth, but the towns are the main attractions and are quite adult. Only so much our DD can take of them.
If you go South coast, the orange elephant is also worth a visit. Play barns and field, animals, maize maze and ice cream (fab in nice weather, but the barns means it’s a good half day activity in the wet).
DM me if you want anymore recommendations.