I think you have to be realistic in terms of how much cultural stuff you will be able to do with kids of that age. Their daily lives are based around satisfying a minimal and predictable set of desires, and when you take them away, that doesn't change. Of course, they can satisfy their need for fun with ice creams and jumping in the pool, but you are probably not going to be lingering on cafe terraces discussing Manet versus Monet with them, and you might feel guilty about doing that with DH even if you have successfully distracted them with a new tablet and some cool games.
As defensive pessimists™, DP and I ended up planning our holidays around keeping the DC happy, and allowing whatever more adult things might come along to happen. Part of that is choosing somewhere that is just lovely whatever you are doing. For example, you could go to Santa Ponsa in Majorca, and stay in the Pirates Village hotel (because if you stay anywhere else in the town, DC will want to know why they're not in that hotel — look it up on Street View), and get the bus to the waterpark over in Magaluf, and look out of the window, and see that it's absolutely gorgeous. And the next day you could go into Palma and take the amazing 100+ year old wooden train to Sóller, where the kids can stand on the platform between carriages, and when it stops on the way for people to take a photo you can see just how amazing the nature is around there.
I mention all of that because I know Majorca well, but there are lots of other places in the Mediterranean where you can combine fun and guaranteed sunshine for the DC with relaxation and a general feeling that life is good. But as PP have pointed out, you can't really be secluded with a beach and lots of eateries within walking distance, because a beach and lots of eateries means lots of people. To some extent you have to embrace at least part of the modern tourism setup, because that's what makes it possible for you to get in a £100 million aeroplane for £100 in the first place. We would all love to do that and also have our own exclusive little bit of the world when we get there, but 150 million people from the northern half of Europe want to do the same thing too, and none of us is more special than any of them. 🙏