Hi fairy1, I'm based in Upper Hutt and was previously in Lower Hutt. Here's some of the activities I know of;
Rimutaka Gymsports (Upper Hutt) has unstructured classes for under 3's and more structured classes for over 3's - or when they are ready for some structure
There are heaps of different Mainly Music locations throughout the Hutt Valley, check out the website and you should be able to find some classes earlier in the week.
Check out the libraries - they offer different options for different ages each week, some music sessions, some craft sessions, some storytelling sessions
Gymbaroo Petone - a bit expensive and you sign up for a term but lots of fun
Check out the local Plunket and Church playgroups. The Salvation Army in Lower Hutt and Petone have really great sessions - I think the Petone one might run on a Wed. And Knox Church on High St, Lower Hutt have great facilities and toys.
I think some of the Lower Hutt kindy's take under 3's, could be worth checking out, but you do drop them off at kindy so means you're not spending the time with him.
And my personal favourite at the moment is Playcentre, so much to do at this age and if your local centre doesn't have appropriate session times for you or you don't like it, try a different centre. You get 3 free visits to see if you like it before enrolling. Sessions are generally about 2.5 hours and the cost is minimal. And best of all you get to play alongside your kid.
Hope you find something you like