Hello OP. I run a tearoom in a tourist area - here's some of the stuff we have learned:
For all those saying stay open later - it's just not cost effective to do so.
We used to open until 5:30. Now we close at 4. The amount of customers you get in that last hour and half you can count on one hand normally. When you add up staff costs, and the overheads for that hour and a half, you are making a loss almost every day.
We have many teas and hot chocolate options and just one good locally roasted coffee. If you are precious about coffee, use a coffee shop, don't come in a teashop and then moan about the coffee...
Unfortunately we have to do the banging thing on the coffee machine.
We do offer a small selection of GF cake but it's not possible (or cost effective) to offer a full GF kitchen.
A lot of the vegan/gf/diabetic/dairy free stuff that people have mentioned is just not possible, there is just so much wastage as the overwhelmingly vast majority of customers won't want it. We know this, we have tried it.
We have loads of different milks. Oat milk sells well.
We offer locally made cakes, scones, teacakes, tarts, traybakes etc. Lunches are jacket potatoes, toasties or sandwiches with small side salad. We have tried lots of other options in the past, but these sell the best for us. We do children's sandwiches on request and have fruit juice and soft drinks available.
We have a couple of wipeable IKEA high chairs.
Tablecloths/linen napkins/soft furnishings are horrible, they get dirty quickly, need a lot of cleaning, not worth it.
Children's toys - just no, difficult to keep clean and the kids run around and upset other customers.
People steal stuff, and break stuff, so don't spend a huge amount on posh crockery and cutlery as you will be constantly replacing it. The mismatched look is nice but a lot of it won't be dishwasher safe. You need hardwearing stuff that will stand being bumped around and put though the dishwasher several times an hour.
We are dog friendly on our covered outside terrace and have outside water bowls and puppuccinos.
Feel free to pm me if you have any questions I haven't covered.