Is the indirect pronoun not always necessary? In these examples shouldn't they all have "le" or "les"?

Question

Can someone explain what is going on here please?

The specific question is why does this sentence not have "les" "El chef sirve comida a los niños."

It seems to me that it should be "El chef les sirve comida a los niños." Duolingo marked it wrong though and Google translate says the les is not necessary either.

Thanks.

Answer 1

There are three situations in which the indirect object pronoun, when the indirect object itself is explicitly mentioned, is required:

• Verbs of the gustar-type
  You cannot say Algo gusta al niño, you must say le gusta al niño
• When the main object comes in front of the verb
  If you say al niño María __ sirve comida, then a le is required. There are even exceptions here, though, as if we are being particularly emphatic about how was being served the food we can omit the pronoun.
• When the main object is a pronoun itself
  In your examples, all the indirect objects are niño or hijos, which are not pronouns. However, if they were él/ella/Vd./mí/ti/etc, then you must include the object pronoun.