Indoor activities for 18 month old.

I'm looking for activities to do with my 18 month old after I pick him up from crèche.

Winter weather means I'm looking for indoor stuff.

We do lots of play with his toys and maybe a few min of a cartoon but hes not that interested.

Should I be doing more learning stuff? Is he ready for crayons.

Basically I'd like to move from the keep him alive stage to the learning (and fun) stage.

Any ideas or books to read.