and how to tell stalagmite and stalactite apart ("Stalactites must hold tight to the roof and stalagmites might join them one day if they grow tall enough)
Omg yes this really stuck in my head. Glad I'm not the only one.
I too remember that!
There was such a wonderful range of characters in the Wishing Chair and Faraway Tree books - pixies, elves, brownies, wizards, talking animals, the Saucepan Man, Dame Washalot, and so on. And the Faraway Tree children weren't middle class.
The Adventure series was my favourite of her series for older children. The four children were very well characterised - you'd never confuse Dinah with Lucy-Ann. And although it's not explicitly stated, the plot of Valley of Adventure was based on RL events in WW2.
And we don't know what Mrs Mannering did, but she was a single working mother who must have had quite a high powered job, and sometimes had problems finding childcare in the school holidays. Quite modern, really.
The original illustrations were great, too. I don't know who illustrated the Faraway Tree books, but he/she really captured the characters and added to the reading experience. And Stuart Tresilian's illustrations for the Adventure books similarly.