Bird Kingdom is a large indoor aviary near the Rainbow Bridge, with tropical birds flying through a multi-level rainforest setting. Niagara Falls is crowded with loud attractions, and this one is still commercial, but it has a gentler rhythm: parrots, lorikeets, reptiles, and small exhibits that work especially well for families or bad-weather afternoons.
It is close enough to Clifton Hill and the riverfront that you can visit without rearranging a day around it. The place is best treated as a secondary stop rather than the reason to come to Niagara Falls, but it gives children and bird-lovers something more tactile than another viewpoint over the gorge.