I have been trying to revitalise our nature studies recently - we've been following Edith Holden's The Country Diary of an Edwardian Lady (which I picked up second hand from Amazon for less than £3) to compare the weather and what she observed when out and about with what we see in our garden and on our dog walks. I've also got hold of a copy of Keeping a Nature Journal from eBay which we've been flicking through from time to time to see how naturalists record their observations in a less formal way. The third thing we've been doing is making more of an effort to keep a nature log of things we see.
However, despite all this planning and provision of resources, it was God's bounty which really got us going yesterday! Whilst walking the dog in some local woods I suddenly spotted a small dead mammal. Dd2 photographed it and we talked about what it was etc. A little later on the walk dd2 accidentally deleted the photograph so we decided to take a diversion on the way home and try to find the little creature again for another photograph to be taken. Eventually we came upon it and took some more photographs. As we were leaving dd2 asked if she could have a dog poo bag, pick up the creature and take it home to show Daddy - well, I was game for this and we brought it home, looked it up in various books and gathered some more information about it. Dd1 wasn't so interested (possibly a bit too sad that it was dead!) so she remembered something she'd seen recently and drew that instead.
Incidentally, if you are interested in studying nature with your children a good place to start is this page of a blog called Handbook of Nature Study. The ideas can easily be used in a small back yard/garden, a public park or a large swathe of countryside!