UK Autumn Child Friendly Sites

Could anyone help recommend a site open at the end of October that has an indoor swimming pool. We live in Northants and so within 3-4 hours would be good. Prefer West Coast but interested to hear about anything that might have activities to keep them entertained. I did consider going to Vendee, France but it's a long haul for maximum of 5 days and so will plan this for next year.