NHM: Birds Gallery
Another NHM "after hours" picture; see some of the specimens in large ("L").
This is the Birds Gallery at the Natural History Museum; it is a very old-fashioned gallery with very few interactive or child-friendly features (which ticks many boxes for me!). It has some wonderful specimens, and is more beautiful than depressing (as sometimes rooms of stuffed animals can be...). It is unfortunate that the birds seems so dusty and faded in comparison to their living relatives; I think that is always the case with (old) birds on display. The Mandarin duck (for instance) would hardly make you want to rush out and see a live one for yourself.
The only display that I really don't enjoy is the one full of hummingbirds: there are 100s of them in one little cabinet making it seem as though someone (a "curiosity collector") must have just been Pokémon-ing hummingbird species ("Gotta catch 'em all") in a rather brutal Victorian fashion.
Eggs, nests, albino birds, zoological illustrations, and skeletons are also on display: it is a small gallery, but more interesting than it looks at first glance!
One of the problems is that it is a very tight bottleneck in the museum's floorplan: it is the only passageway between the Waterhouse Building and The Red Zone so gets super-crowded. Much better early or late in the day.
Most of the museum's bird collection is actually at the site in Tring; apparently it is wonderful, but I haven't yet visited... The museum no longer collects bird specimens, but the ornithologists are actively involved in conservation.