For the whole of summer holidays Fife Council offer free swimming at all the leisure centres for anyone under 17 years old. No purchase necessary.
Offer available 7 days per week: Mon-Friday (10am - 5pm) and Weekends (9am to 5pm). Available for school holidays (30th June - 19th August).
See fifeleisure.org.uk for list of locations.
Offer is run by Fife Council but similar offers may be available at other local authorities so might be worthy checking out your local council leisure centres website.