como las de los cuento de hadas

[Tyrn]

Hi,

Y así habían seguido por ese túnel y habían
encontrado una puerta, una diminuta puerta de
madera de apenas metro y medio de altura, como
las de los cuento de hadas.

Why not de los cuentos or del cuento?

[Rusty]

Doing an online search for both 'los cuentos de hadas" and "los cuento de hadas" reveals that the latter is indeed used, but is less common.
At first glance, the latter appears to be a typo. However, some may think that 'cuento de hadas' is an expression (set phrase / locution) and is therefore made plural by only a change in the article.
Let's see what a native speaker has to say.

[AngelicaDeAlquezar]

Another typo. There must be an agreement between article ("los") and noun ("cuentos").

It must have been "como las de los cuentos de hadas".

It couldn't have been "como las del cuento de hadas", because there is no explicit reference to a previous fairy tale having been told to the reader and there isn't only one fairy tale in the world.