Hello! Sorry to be late to this thread. I grew up in St Andrews and it has made me quite homesick.
I know of a cafe in London that sounds like it has a similar vibe to the one you are aiming for, and the thing they do that I really like is offer all sandwiches as salads and vice versa - so you can have falafel and humous on pita bread or with cucumber, tomato, avocado and salad. Ditto chicken and avocado; ham and cheese; smoked salmon and cream cheese; spinach, garlic mushroom, red onion and parmesan (with optional crispy bacon, mmmm). Cheese and (delicious, home-made) pickle becomes a ploughman's. Actually all of these are good with extra avocado too. All the soups are home-made and the cakes baked at home by friends of the cafe. They also serve babycinos ('fluffies' elsewhere on this thread) and have a box of toys and photocopies of really good part-started drawings for children to finish, done by local art students (underneath this cafe is a gallery so this is kind of their theme).
If possible, I would consider doing a 'tasting plate' of cakes, ie slivers of a selection of them. The cafe I mention above always did one cake served in tiny portions, eg flapjacks or brownies, for about 40p a go, so you could have a bite of something sweet with your coffee or give one to your toddler.
Also, I recommend these tea bags which are completely delicious.
Good luck with this - it sounds brilliant. Well done for getting off to such a great start.