Need some rainy day ideas for East Devon/West Dorset with 4 yr old!

[PorridgeAgainAbney]

We're going next week and the forecast is a bit shit! I've got a lot of ideas of things to do if the weather is dry, but so far my only options on rainy days are the Dinosaur Museum in Lyme Regis, and in Exeter the Royal Albert museum and underground passages and maybe a train or bus trip.
We're on a pretty tight budget so really I wondered if anyone has any ideas for quite normal things to do - eg, nice swimming pools/activity centres, soft play - as well as bigger specific destinations.
Ideally within 1 hour drive of Axminster. Thanks

The swimming pool at Ladram Bay holiday park is lovely for younger ones, and you can use the parks playarea, small soft play and cafe etc. It's £5 to "park" and you pay for swimming but other bits are free.

Bicton Park has indoor play area and large outdoor play area, they used to take Tesco vouchers.

Big soft play Exmouth Seafront Ocean with bowling ally, and swimming pool in town is good with a climbing wall. Also "younger" suit 4yr old soft play in Exmouth town centre called Sams.

Trampoline indoor centre I bounce in Exeter.

Crealy is the bigger activity park but more expensive.