We go to Costa for a babycinno (it is a rainy day treat after the library, if the sun is shining however we go to the park instead). It only costs 50p there
My three are older than Freddie, and are all now school age. But we have been doing free or cheap activities for years!
They all went to our local toddler group, which cost £1 per week per family. I had to pay the small price of being Treasurer for 2 years, but it was an experience fun.
They all still enjoy going to the library, but when they were pre-school age they used to go to the story sessions there too, which were free.
Now they are getting older they love the local museum, which is free. DD(4) loves the Victorian dresses and the puppets, DS1(7) loves the ships exhibition and DS2(6) loves the archaeology section which has "a real live skeleton" (apparently).
Then there is the castle ruins, which have a lovely park next to them, and are right by the sea so you can look out for invading ships coming over the horizon .
Then there is the beach, which is miles of unspoilt sand dunes. You have to pay to park, but a 12 month parking pass costs about £5.
Then there is the forest visitor centre, with red kite feeding every afternoon, 2 playgrounds and lots of forest walks. Again, you pay to park but it only costs £15 a year.
A trip to the park/beach/forest/castle usually involves a picnic, which is far cheaper than buying food in a cafe.
Swimming is free here during school holidays (it is just avoiding spending in the vending machines on the way out that is problematic!).
We do pay for riding for DD (£10 a fortnight) and piano lessons for DS1 (£10 a week). They also go to Urdd which is £1 each a week and £18 a year membership between them. DS1 plays football for the under 11 team, which costs £15 a year to sign on with the league. DS2 goes to under 7's football, which is free. DS1 plays hockey, which is free at the moment as he only trains with them but will cost £10 a year if he signs on with the league.
I suppose the costs of those do mount up, but we didn't pay that much when they were toddlers.