I think you need to rename the thread as a trip to Anglesey is not what all UK holidays are like. But if it’s any consolation, all my memories of childhood holidays in Wales are being wet and cold.
Seriously if you did check the place out before you booked then you should not be surprised your cold and bored. Plus Wales has been very strict with restrictions during covid. Do you understand Wales is not actually in England? I’m not saying that to call you ignorant, many English people do not understand that they are not one and the same and England’s rules re covid don’t apply.
There are lots of holiday destinations in the UK you would have been better off for warmth and things to do if you wanted more than outdoor walks and scenery. The south of England for starters, Cornwall, Devon especially if you wanted hot days lounging on a beach. You have a bunch of theme parks all over the country, most of which teenagers would love, holiday parks that provide entertainment, cities that are full of culture and history.
You havnt said where you live, for some reason I’m guessing London, no idea why, but if your heading back then maybe look at doing a detour first and having some fun. I’m a particular fan of Liverpool, love the city the culture, people, food. They have an Aqua park at the docs your teenagers would love, lots of places over the uk have these, great shopping and there is bound to be other stuff going on. Maybe do a detour to Alton Towers, Thorpe Park or any other place where your kids can let their hair down and have fun, there are lot of go ape type places too.