RSPB Otmoor is a wetland reserve a couple of miles from Oxford. The area, originally marshland, was drained and used for arable farming until the 1990s. Since 1997 the RSPB have been returning the farmland to reedbeds and wet meadows. This has involved the planting of over 150,000 reed seedlings by hand!
Otmoor reserve is in a remote area (for Oxfordshire) and has limited visitor facilities. Despite this, I'd still recommend a visit to families, as it has some amazing bird watching opportunities.
We visited at the weekend, and for once it wasn't raining. There are several rights of way around the area but as most of the surrounding fields were flooded we quickly decided on the 1.5 mile visitor trail. This takes in the main bird hide and a couple of screened viewing areas.