Lots of play and role play - arts and crafts, gardening, cooking and music. That's what my son does at his nursery. I'm sure the nursery which your ds will go to will welcome you for a visit just to see it in action.
My DS is 4 and has been at nursery since he was 2 yrs 10 mths. It's been great for him. The main benefits for my DS have been:
Socialising with other children. Getting into a good routine Having access to lots of different toys and activities, and a playground.
I wasn't a great 'Blue Peter Presenter' SAHM (the temptations of staying in PJs and pottering around house were too great!), so couldn't have provided everything the nursery do.
This week at nursery, they've been working on their gardening project, had a visit from a theatre company, had water play in the mornings and have been doing lots of crafty things indoors during the hottest part of the day.
dd's goes to nursery (full time) which takes them to the local library and museum etc using the 'walkodile'. so they are also learning road sense as well as learning. they took them to see the a Regimental Parade from a unit returning from Afghanistan.
they do 'yogabugs' too and she shows us the moves every now and then.
they bring in a musician from the Sage outreach.
So stuff I would never had been able to do with them normally.
Maybe these things things can help you look laterally at what you can offer them locally?
We have a family park to the wetlands sanctuary nearby and they run activities with the seasons there plus it is a great place all round for you to pass on your own wildlife knowledge.
the Gala Theatre in Durham also has drama events for younger children which you cna also go to.