I find some parts of Mallorca quite expensive for eating out, at least as much as the UK, noticeably more than mainland Spain or the Canaries, although alcoholic drinks are usually cheaper.
Having said that, I think B&B and some eating out can be cheaper than nice AI, but a better experience than buffet AI, which isn't very relaxing, I like to eat outside and be served at a table on the seafront, or in a nice square.
We normally stay SC or B&B in an apartment, so we can stock up on drinks, snacks, ice creams and food for lunches, BBQs, nibbles etc. We then usually have a big breakfast maybe at about 9 to 10 am and then either have lunch at a restaurant mid afternoon while out and about and then something like cheese, ham, bread, olives, crisps etc on the balcony in the evening, or we might go out for a drink and a few tapas. Or we might just have a slice of pizza, ice cream or sandwich in the daytime, then have a meal out in the evening or a BBQ. So we only pay for one full restaurant meal on both days, and the rest of the food is at supermarket prices.
But then if it's just you and a 9 YO and he wants to meet other kids, you might want to stay in a hotel/apartment complex with a communal pool, activities etc, so he can entertain himself some of the time. Although that shouldn't tie you to AI, there's lots of accommodation with these facilities but also any sort of food provision from SC to AI.