I'm looking about for inspiration as well - 3 children aged 8 months-6yrs. Don't like in the Midlands... I'm in Surrey/Hampshire border area. Just started on making a list which I've put on my local residents website in the hope that other parents/carers will suggest things.
I hope it will be reasonable weather as when it's wet it can be hard to find things to do - well, there is always sorting out the toys at home!
There is indoor crazy golf at star city near Birmingham, could be good for a rainy day. Warwick castle is great when they have the jousting etc on, though it's a bit expensive so I try to find vouchers when we go.