¿Por qué "a los"?

[BobRitter]

LearnWithOliver.com dice:

A los ratones les gusta el queso.

Mice like cheese.

¿Por qué "A los". Los ratones no son personas o mascotas.

Como siempre gracias a todos.

[poli]

Because in Spanish this translates as cheese pleases the mice.

A person better versed in Spanish grammar will let you know why the "a" is always used in these cases (other example: a mí me gustan las papas fritas).
It may have something to do with the personal a rule.

[Rusty]

We are not talking about a personal 'a' here, but the preposition 'a'.
The 'a' introduces the indirect object. This is always the case.

Another way to formulate the transliteration is "(The) cheese is pleasing to the mice." Here it's plain to see that 'to' translates directly to Spanish as 'a,' and that it is introducing an indirect object ('to the mice' is the indirect object, answering the question, 'To whom is the cheese pleasing?').

[AngelicaDeAlquezar]

I agree with Rusty.

The subject is the thing that is pleasing and I am the (Indirect) object to whom it is pleasing. This can be seen in the part of the sentence with whom the verb agrees.
The preposition "a" introduces the object and we also often need an object pronoun too.

In the next examples, the second sentence might be clearer about the structure. We don't always speak like that, because we prefer to stress the person that is affected by the verb than the thing that causes the effect.

- (A mí) me gusta el aroma de las flores. / El aroma de las flores me gusta (a mí).
I like the smell of (the) flowers
- ¿(A ti) no te gusta el café? / ¿El café no te gusta (a ti)?
You don't like coffee?
- A Yolanda le gustan las fiestas. / Las fiestas le gustan a Yolanda.
Yolanda likes parties.
- A Luis le gustas (tú). / (Tú) le gustas a Luis.
Luis likes you.
- Al perro no le gustan esas croquetas. / Esas croquetas no le gustan al perro.
The dog doesn't like that dog food.
- A nosotros nos gusta el silencio. / El silencio nos gusta (a nosotros).
We like silence.
- ¿A ustedes les gusta estar en casa? / ¿Estar en casa les gusta (a ustedes)?
Do you like being at home?
- A los empresarios no les gustan los impuestos. / Los impuestos no les gustan a los empresarios.
Business people don't like taxes.
- A las abejas les gusta lo dulce. / Lo dulce les gusta a las abejas.
Bees like what is sweet.

[babymetal]

Like said before, the preposition a introduces the indirect object, but also bear in mind that the indirect object is not always named. Here is an example.

¿Te acuerdas de la mujer a la que pedimos una almohada en el avión?

This is a more complex sentence, but it's something to bear in mind. Basically, the indirect object can be represented in many different forms.

[BobRitter]

Gracias a todos.