We went to the new Thomasland at Drayton Manor this week and it was fab!
There are about 10 rides - all suitable for under 5s, and an enormous indoor soft play area. DD1 (5) had the best time going on the Troublesome Trucks rollercoaster (and everything else!) DD2 (nearly 1) was in heaven in the soft play.
Definitely worth going to, particularly if you have teenagers who want to explore the rest of Drayton Manor.