A sweet Dahlian short story. There is lots that's whimsical (the names of the monsters, that there are teeny tiny people living in trees). Everything happens very quickly to a sweet ending.
There were lots of little details that even out-of-reality felt like he was drawing from real life, like the idea that robins love children, the childlike experience of going 'what if I could fly on birds?' the wish fulfilment of 'what if my friends came after bedtime to see me?'. Purely speculation but I wonder if when he is talking about people living in clouds that was something he actually thought about and came up with while he was flying planes, or the description on birds on a lake from far above.