HI Blossom Salcombe is a beautiful town and there is plenty to do both in summer and winter. There's a great soft play café for little ones, crabbing, lovely pubs and restaurants, beautiful beaches.
We live in a village less than 10 minutes away from Salcombe and love visiting in the winter. However, we avoid it like the plague in the summer because it is rife with tourists and second home owners. It probably is on a parr with St Ives in the summer. We definitely wouldn't want to live there.
Kingsbridge is a lovely town with lots to do for little ones, there's a leisure centre with a big pool and kiddies pool, swimming lessons, a gym, lots of exercise classes. There's a pottery painting café, another soft play with kiddies hair dressers. It's still on the water so very pretty. There's loads of seasonal things going on like fair week, a food and music festival, farmers markets etc. Guides, brownies, cubs scouts etc. Most of the villages in the area have their own village hall and with this baby/toddler groups.
Take a look at Kingsbridge and some surrounding villages such as Chillington and Malborough. Salcombe is the town that everyone knows, but because of the huge influx of visitors and second home owners the housing market has been priced far out of most of the locals price range. You may also find that lots of the houses you would be looking at have a Devon covenant on them, so you have to have lived and worked in the area for the last 3 years...
I've never used the post office in Salcombe, but the Kingsbridge one is fairly big and could cope with what you need it to.