I liked this page on Wildlife Equipment for Kids by the Wildlife Gardener. It recommends:

• Gardening Tools “with wildlife gardening, the chances are that your child is going to be far more interested in the wildlife than the actual gardening”
• Magnifying Glass “envaluable for enabling them to distinguish and differentiate between the species”
• Microscope
• Binoculars
• Tape Recorder “A small tape recorder such as a dictaphone can be very useful for recording the sound of birdsong”