One thing that works really well in choosing songs (especially in Nursery) is to invite a "visitor" for singing time. When I first started working in Nursery it was wintertime, so I invited a stuffed snowman similar to this one to choose our songs:
Sometimes I would do a voice for him and have him talk directly to the children, other times I have him whisper in my ear. The little kids LOVED it! I have penguin one for winter too.
You could adapt this for any season. I brought a Leprachaun for March and a bunny for spring.
I went to the local $ store and purchased a few puppets a ladybug, a bee, a frog etc. for summer (although I haven't used them yet because we have our Primary Chorister coming in now.)
You could easily find a scarecrow or pumkin or something for fall. Really fun!