"a" is needed for people and animate beings, e.g. animals, pets. I see my sister - Veo a mi hermana. I see the window - veo la ventana. A can join with 'el' to make 'al' as in Veo al hermano de su esposa - I see the brother of your wife. "A" can also mean "to" as in to/toward. As in your text above (maybe I got confused - it's been 25 years). " Le gusta' means "is pleasing to". It is not my son who likes something in Spanish, rather it is 'the .... is pleasing to my son" A mi hijo le gusta uvas. To my son is pleasing grapes/ My son likes grapes.

Muchos Gracias!

Hi Paul. In your sentence the "a" is needed to indicate who is the affected person by the action that the verb expresses. (when we refer to the indirect object) A mi hijo le gusta mi carro. Always when the indirect object is mentioned explicitly it must be accompanied by the preposition "a", whether they are people, animals or inanimate objects, in this case the preposition "a" can not be omitted. A mi hijo le gusta mi carro. A mi hijo y a mi sobrino les gusta mi carro. A ellos les gusta mi carro. Le escribí una carta a mi hija. Le regalé una blusa a María. A mi perro le duele una pata. Le quebré una pata a la mesa. Le agregué una recámara a la casa. The preposition "a" can be omitted if the indirect object is not mentioned explicitly, because it was already mentioned previously or because it is understood by the context. Le gusta mi carro. (a mi hijo) Les gusta mi carro. (a mi hijo y a mi sobrino) Les gusta mi carro. (a ellos) Le escribí una carta. (a mi hija) Le regalé una blusa. (a María) Le duele una pata. (a mi perro) Le quebré una pata. (a la mesa) Le agregué una recámara. (a la casa) The preposition "a" can also be omitted when we talk about inanimate objects, but when we refer to the direct object. Veo la ventana. Compré una casa. Pinté mi carro. Escribí una carta. Regalé muchos dulces. I hope this helps.