I'm going to answer the question asked rather than get into the idea of whether it's about money or not. Of course there are lots of cheap/free things like going to the park and playing pooh sticks/backing/arts and crafts...
@Greenbutterlfy566 we have a teen and child similar age to you.
The highlight last year was body boarding in Tenby followed by an amazing pizza meal after
Things on the list for this year: Tower of London and National History Museum (been to both before)
General things over the years: National trust membership, bucket and spade holidays, lots of in and outdoor play areas, zoo, farm park, water park, theme parks (Merlin via Merlin passes and others e.g. Paultons), steam fair, Bonfire night, going in a camping pod and being able to roast marshmallows over the fire, Portsmouth Dockyard, train trips to London, steam trains, Days out with Thomas, taking the Hovercraft to IOW, castles, art galleries (Tate or Buck Palace or Royal Academy of Arts, National Gallery).
Hope you have lots of fun!